UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Investment Company Act File Number: 811-05986

T. Rowe Price Index Trust, Inc.

(Exact name of registrant as specified in charter)

100 East Pratt Street, Baltimore, MD 21202

(Address of principal executive offices)

David Oestreicher

100 East Pratt Street, Baltimore, MD 21202

(Name and address of agent for service)

Registrant’s telephone number, including area code: (410) 345-2000

Date of fiscal year end: December 31

Date of reporting period: June 30, 2018

*Certain mutual fund accounts that are assessed an annual account service fee can also save money by switching to e-delivery.

U.S. stocks recorded decent gains in the first half of 2018, but unlike last year, investors had to absorb some bumps along the way. In February, volatility spiked and the S&P 500 Index briefly tumbled over 10% from its highs, putting it in correction territory. The major U.S. benchmarks recovered their losses in the spring, eventually bringing the technology-focused Nasdaq Composite Index and the smaller-cap indexes to new highs. Volatility stayed somewhat elevated, however, and many investors clearly remained anxious as the first half of your fund’s fiscal year ended.

Solid corporate and economic fundamentals initially seemed to promise that 2017’s strong stock market momentum might carry forward into 2018. Continued global synchronized growth led to strong profits for many multinationals. In the U.S., earnings for the S&P 500 rose by nearly 25% in the first quarter versus a year before, according to FactSet—the best performance since the recovery from the financial crisis. Profit growth also picked up in Europe, Japan, and emerging markets, even as growth in many international economies cooled a bit.

Inflation fears presented the first obstacle to the markets in February, however. Stocks tumbled on news that hourly wages had jumped in January, sparking fears that the Federal Reserve would pick up its pace of interest rate increases in order to head off inflation. Wage growth moderated in the following months, but a series of strong economic reports raised growth expectations and sent long-term interest rates to multiyear peaks by May. Investors also worried that the massive U.S. fiscal stimulus from December’s tax cuts and March’s spending bill might overheat the economy, though interest rates fell back in late May and June as Fed officials stressed their intention to move slowly in tightening monetary policy.

Trade tensions soon emerged as a second impediment for the markets. The Trump administration began implementing a more populist trade stance in March, announcing tariffs on steel and aluminum imports, threatening to withdraw from the North American Free Trade Agreement (NAFTA), and later raising the possibility of taxing auto imports. The administration also announced a steady escalation in possible tariffs on Chinese goods, eventually targeting a list of $200 billion in Chinese imports. China and other U.S. trading partners vowed to retaliate proportionately.

Investors initially seemed willing to dismiss the tit-for-tat threats as negotiating tactics, but evidence eventually emerged that even the prospect of tariffs was impacting corporate strategies and profit outlooks. Stocks slumped on June 21, after German automaker Daimler lowered its earnings guidance due to possible tariff increases on SUVs it manufactures in the U.S. and sells in China. A few days later, Harley-Davidson revealed that it was planning to move some of its motorcycle production to Europe to avoid retaliatory tariffs recently announced by the European Union.

Boeing, Caterpillar, and other leading exporters suffered declines as trade tensions worsened, but small-caps, which typically have far less international exposure, fared much better than large-caps in the first half of the year. Growth shares continued to outperform value shares despite the strong performance of energy stocks, which benefited from a rise in oil prices to multiyear highs. Stocks in overseas markets reacted particularly poorly to growing trade fears and fell for the period. A decline in many currencies relative to the dollar also weighed on international bond and stock returns for U.S. investors.

Meanwhile, technology shares continued to dominate, with much of the market’s overall gain to date in 2018 concentrated in a handful of mega-cap companies able to leverage dominant Internet platforms. Data breaches and concerns about the growing power of these firms resulted in calls for government intervention in early 2018. For now, however, the threat of increased regulation seems a longer-term one that appears minor in comparison to the powerful fundamental strength of these companies.

T. Rowe Price’s global team of industry experts is monitoring the possible impact of tariffs and other challenges on a wide range of companies—from the global tech titans to small, domestic firms that get little analyst coverage on Wall Street. While the rest of 2018 may bring further surprises, you can rest assured that your portfolio manager is drawing on a wide range of insights in seeking to provide shareholders with superior returns while minimizing the impact of unforeseen political events or other pitfalls.

The fund seeks to track the performance of a benchmark index that measures the investment return of large-capitalization U.S. stocks.

The Equity Index 500 Fund returned 2.54% in the six-month period ended June 30, 2018, versus 2.65% for the S&P 500 Index. (Performance will vary for the I Class shares, reflecting their different fee structure. Past performance cannot guarantee future results.) Fund performance tends to slightly lag that of the broader index due to operating and management expenses.

The fund uses a full replication strategy so that the weightings of our holdings match those of the S&P 500 Index. Six of the sectors recorded positive results, and five sectors posted losses for the six-month period. The consumer discretionary and information technology sectors led, and the consumer staples and telecommunication services sectors lagged. The lion’s share of the gains came from just a few stocks, including consumer discretionary stocks Amazon.com and Netflix and technology stocks Microsoft and Apple. Technology shares suffered large losses in February during a market correction, but they rebounded strongly. The fund’s performance was also helped by the information technology sector’s large weighting, representing 26% of the S&P 500. Fierce competition, a challenging regulatory environment, as well as a rising interest rate environment hurt the telecommunication services sector. AT&T and Verizon Communications performed poorly. Deflationary pricing, trade concerns, and increased transportation costs weighed on consumer staples stocks. Walmart and General Mills did not perform well. (Please refer to the portfolio of investments for a complete list of holdings and the amount each represents in the portfolio.)

The Total Equity Market Index Fund returned 3.02% for the six-month period ended June 30, 2018, versus 3.25% for its benchmark, the S&P Total Market Index. (Past performance cannot guarantee future results.) Fund performance tends to slightly lag that of the benchmark because of the fund’s operating and management expenses.

The fund uses a sampling strategy. Six of the sectors recorded positive results, and five sectors posted losses for the six-month period. Amazon.com, Netflix, Microsoft, Apple, Alphabet, and Facebook accounted for almost all of the gains. After the S&P 500 reached an all-time high in late January, the index drifted lower as declines in the financials and consumer staples sectors weighed on performance. An environment where short-term interest rates rose more than long-term rates dragged down financials while deflationary pricing and increased competitive pressures hurt the performance of consumer staples stocks. Information technology and consumer discretionary stocks rebounded from February lows, but their gains were offset by poor performance in many other sectors. Some of the worst-performing stocks included tobacco products maker Philip Morris, pharmaceutical company Johnson & Johnson, AT&T, Comcast, and consumer goods company Procter & Gamble. (Please refer to the portfolio of investments for a complete list of holdings and the amount each represents in the portfolio.)

The fund seeks to track the performance of a benchmark index that measures the investment return of small- and mid-capitalization U.S. stocks.

The Extended Equity Market Index Fund returned 5.99% for the six-month period ended June 30, 2018, versus 6.07% for its benchmark, the S&P Completion Index. Past performance cannot guarantee future results. Fund performance tends to slightly lag that of the benchmark because of the fund’s operating and management expenses.

The health care, information technology, and energy sectors advanced the most. The telecommunication services, materials, and industrials and business services sectors posted losses. The outperformance of biotechnology stocks boosted the health care sector, as investors appeared to be in a risk-on mood for shares in companies that use live organisms to manufacture medicines. Sarepta Therapeutics, June Therapeutics, and Loxo Oncology were standout biotechnology stock performers. Performance was also strong in the information technology sector. Mobile gaming publisher Glu Mobile, global software services company Unisys, and precision instruments maker Mesa Labs all performed well. Telecommunication services lagged in the period. Fierce competition and a challenging regulatory environment, as well as rising interest rates, hurt the sector. Sprint, Globalstar, and Shenandoah Telecommunications performed poorly. (Please refer to the portfolio of investments for a complete list of holdings and the amount each represents in the portfolio.)

T. Rowe Price’s Equity Market Index Funds are designed for investors who want to harness the potential for long-term capital appreciation from broad exposure to large-cap stocks (Equity Index 500 Fund), small- and mid-cap stocks (Extended Equity Market Index Fund), or the entire U.S. stock market (Total Equity Market Index Fund). These funds could serve as core holdings in an investor’s portfolio, as they offer attributes that many investors will find appealing.

They are well diversified, which can reduce the potentially negative impact of a given stock on the entire portfolio. The Equity Index 500 Fund invests in all S&P 500 Index stocks while the Total Equity Market Index Fund and the Extended Equity Market Index Fund owned 1,298 and 1,578 holdings, respectively, as of June 30, 2018. (Diversification cannot assure a profit or protect against loss in a declining market.)

The funds tend to closely track their benchmarks. The Equity Index 500 Fund uses a full replication strategy so that the weightings of our holdings match those of the S&P 500 Index. The Total Equity Market Index Fund and the Extended Equity Market Index Fund use a sampling strategy to approximate the sector allocations, price-to-earnings ratio, and other attributes of their benchmarks. We occasionally invest in securities such as futures and exchange-traded funds so that the index funds can accommodate cash flows and remain fully invested.

They offer instant, broad exposure to different sectors of the stock market, and each fund’s sector allocations are consistent with its benchmark’s sector breakdown. Accordingly, changes in the funds’ sector diversification and other overall characteristics reflect changes in the composition of the indexes, rather than strategic shifts that are typical of an actively managed fund. Since the funds are designed to track their respective indexes, they do not have the flexibility to shift assets toward stocks or sectors that are rising or away from those that are declining.

We believe the U.S. is in the later stages of economic and market cycles. In the near term, we acknowledge that strong earnings growth could continue to buttress stocks, and we believe that equities gains could be fueled by a narrow list of winning stocks. In the intermediate term, we are mindful of potential risks from slowing economic growth, geopolitical shocks, rising oil prices, higher inflation, tight labor markets, and protectionist trade policies. We believe the Federal Reserve is likely to continue with further rate hikes in 2018, but at a measured pace.

The views expressed reflect the opinions of T. Rowe Price as of the date of this report and are subject to change based on changes in market, economic, or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

As with all stock mutual funds, the funds’ share prices can fall because of weakness in the stock market, a particular industry, or specific holdings. Stock markets can decline for many reasons, including adverse political or economic developments, changes in investor psychology, or heavy institutional selling. The prospects for an industry or company may deteriorate because of a variety of factors, including disappointing earnings or changes in the competitive environment.

This chart shows the value of a hypothetical $10,000 investment in the fund over the past 10 fiscal year periods or since inception (for funds lacking 10-year records). The result is compared with benchmarks, which includes a broad-based market index and may also include a peer group average or index. Market indexes do not include expenses, which are deducted from fund returns as well as mutual fund averages and indexes.

As a mutual fund shareholder, you may incur two types of costs: (1) transaction costs, such as redemption fees or sales loads, and (2) ongoing costs, including management fees, distribution and service (12b-1) fees, and other fund expenses. The following example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds. The example is based on an investment of $1,000 invested at the beginning of the most recent six-month period and held for the entire period.

Please note that the Equity Index 500 Fund has two share classes: The original share class (Investor Class) charges no distribution and service (12b-1) fee, and I Class shares are also available to institutionally oriented clients and impose no 12b-1 or administrative fee payment. Each share class is presented separately in the table.

Actual Expenses
The first line of the following table (Actual) provides information about actual account values and actual expenses. You may use the information on this line, together with your account balance, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number on the first line under the heading “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes
The information on the second line of the table (Hypothetical) is based on hypothetical account values and expenses derived from the fund’s actual expense ratio and an assumed 5% per year rate of return before expenses (not the fund’s actual return). You may compare the ongoing costs of investing in the fund with other funds by contrasting this 5% hypothetical example and the 5% hypothetical examples that appear in the shareholder reports of the other funds. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period.

Note: T. Rowe Price charges an account service fee that is not included in the accompanying table. The account service fee is charged on a quarterly basis, usually during the last week of a calendar quarter, and applies to accounts with balances below $10,000 on the day of the assessment. The fee is charged to accounts that fall below $10,000 for any reason, including market fluctuations, redemptions, or exchanges. When an account with less than $10,000 is closed either through redemption or exchange, the fee is charged and deducted from the proceeds. The fee applies to IRAs but not to retirement plans directly registered with T. Rowe Price Services or accounts maintained by intermediaries through NSCC^®Networking. If you are subject to the fee, keep it in mind when you are estimating the ongoing expenses of investing in the fund and when comparing the expenses of this fund with other funds.

You should also be aware that the expenses shown in the table highlight only your ongoing costs and do not reflect any transaction costs, such as redemption fees or sales loads. Therefore, the second line of the table is useful in comparing ongoing costs only and will not help you determine the relative total costs of owning different funds. To the extent a fund charges transaction costs, however, the total cost of owning that fund is higher.

T. Rowe Price Index Trust, Inc. (the corporation) is registered under the Investment Company Act of 1940 (the 1940 Act). The Equity Index 500 Fund (the fund) is a diversified, open-end management investment company established by the corporation. The fund seeks to track the performance of a benchmark index that measures the investment return of large-capitalization U.S. stocks. The fund has two classes of shares: the Equity Index 500 Fund (Investor Class) and the Equity Index 500 Fund–I Class (I Class). I Class shares generally are available only to investors meeting a $1,000,000 minimum investment or certain other criteria. Each class has exclusive voting rights on matters related solely to that class; separate voting rights on matters that relate to both classes; and, in all other respects, the same rights and obligations as the other class.

Basis of Preparation The fund is an investment company and follows accounting and reporting guidance in the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946 (ASC 946). The accompanying financial statements were prepared in accordance with accounting principles generally accepted in the United States of America (GAAP), including, but not limited to, ASC 946. GAAP requires the use of estimates made by management. Management believes that estimates and valuations are appropriate; however, actual results may differ from those estimates, and the valuations reflected in the accompanying financial statements may differ from the value ultimately realized upon sale or maturity.

Investment Transactions, Investment Income, and Distributions Investment transactions are accounted for on the trade date basis. Income and expenses are recorded on the accrual basis. Realized gains and losses are reported on the identified cost basis. Premiums and discounts on debt securities are amortized for financial reporting purposes. Dividends received from mutual fund investments are reflected as dividend income; capital gain distributions are reflected as realized gain/loss. Dividend income and capital gain distributions are recorded on the ex-dividend date. Income tax-related interest and penalties, if incurred, are recorded as income tax expense. Distributions from REITs are initially recorded as dividend income and, to the extent such represent a return of capital or capital gain for tax purposes, are reclassified when such information becomes available. Income distributions, if any, are declared and paid by each class quarterly. Distributions to shareholders are recorded on the ex-dividend date. A capital gain distribution may also be declared and paid by the fund annually.

Class Accounting Shareholder servicing, prospectus, and shareholder report expenses incurred by each class are charged directly to the class to which they relate. Expenses common to both classes, investment income, and realized and unrealized gains and losses are allocated to the classes based upon the relative daily net assets of each class. To the extent any expenses are waived or reimbursed in accordance with an expense limitation (see Note 6), the waiver or reimbursement is charged to the applicable class or allocated across the classes in the same manner as the related expense.

Redemption Fees A 0.5% fee is assessed on redemptions of fund shares held for 90 days or less to deter short-term trading and to protect the interests of long-term shareholders. Redemption fees are withheld from proceeds that shareholders receive from the sale or exchange of fund shares. The fees are paid to the fund and are recorded as an increase to paid-in capital. The fees may cause the redemption price per share to differ from the net asset value per share.

In-Kind Redemptions In accordance with guidelines described in the fund’s prospectus, and when considered to be in the best interest of all shareholders, the fund may distribute portfolio securities rather than cash as payment for a redemption of fund shares (in-kind redemption). Gains and losses realized on in-kind redemptions are not recognized for tax purposes and are reclassified from undistributed realized gain (loss) to paid-in capital. During the six months ended June 30, 2018, the fund realized $837,432,000 of net gain on $1,240,462,000 of in-kind redemptions.

New Accounting Guidance In March 2017, the FASB issued amended guidance to shorten the amortization period for certain callable debt securities held at a premium. The guidance is effective for fiscal years and interim periods beginning after December 15, 2018. Adoption will have no effect on the fund’s net assets or results of operations.

Indemnification In the normal course of business, the fund may provide indemnification in connection with its officers and directors, service providers, and/or private company investments. The fund’s maximum exposure under these arrangements is unknown; however, the risk of material loss is currently considered to be remote.

The fund’s financial instruments are valued and each class's net asset value (NAV) per share is computed at the close of the New York Stock Exchange (NYSE), normally 4 p.m. ET, each day the NYSE is open for business. However, the NAV per share may be calculated at a time other than the normal close of the NYSE if trading on the NYSE is restricted, if the NYSE closes earlier, or as may be permitted by the SEC.

Fair Value The fund’s financial instruments are reported at fair value, which GAAP defines as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The T. Rowe Price Valuation Committee (the Valuation Committee) is an internal committee that has been delegated certain responsibilities by the fund’s Board of Directors (the Board) to ensure that financial instruments are appropriately priced at fair value in accordance with GAAP and the 1940 Act. Subject to oversight by the Board, the Valuation Committee develops and oversees pricing-related policies and procedures and approves all fair value determinations. Specifically, the Valuation Committee establishes procedures to value securities; determines pricing techniques, sources, and persons eligible to effect fair value pricing actions; oversees the selection, services, and performance of pricing vendors; oversees valuation-related business continuity practices; and provides guidance on internal controls and valuation-related matters. The Valuation Committee reports to the Board and has representation from legal, portfolio management and trading, operations, risk management, and the fund’s treasurer.

Various valuation techniques and inputs are used to determine the fair value of financial instruments. GAAP establishes the following fair value hierarchy that categorizes the inputs used to measure fair value:

Level 1 - quoted prices (unadjusted) in active markets for identical financial instruments that the fund can access at the reporting date

Level 2 - inputs other than Level 1 quoted prices that are observable, either directly or indirectly (including, but not limited to, quoted prices for similar financial instruments in active markets, quoted prices for identical or similar financial instruments in inactive markets, interest rates and yield curves, implied volatilities, and credit spreads)

Observable inputs are developed using market data, such as publicly available information about actual events or transactions, and reflect the assumptions that market participants would use to price the financial instrument. Unobservable inputs are those for which market data are not available and are developed using the best information available about the assumptions that market participants would use to price the financial instrument. GAAP requires valuation techniques to maximize the use of relevant observable inputs and minimize the use of unobservable inputs. When multiple inputs are used to derive fair value, the financial instrument is assigned to the level within the fair value hierarchy based on the lowest-level input that is significant to the fair value of the financial instrument. Input levels are not necessarily an indication of the risk or liquidity associated with financial instruments at that level but rather the degree of judgment used in determining those values.

Valuation Techniques Equity securities listed or regularly traded on a securities exchange or in the over-the-counter (OTC) market are valued at the last quoted sale price or, for certain markets, the official closing price at the time the valuations are made. OTC Bulletin Board securities are valued at the mean of the closing bid and asked prices. A security that is listed or traded on more than one exchange is valued at the quotation on the exchange determined to be the primary market for such security. Listed securities not traded on a particular day are valued at the mean of the closing bid and asked prices. Actively traded equity securities listed on a domestic exchange generally are categorized in Level 1 of the fair value hierarchy. OTC Bulletin Board securities, certain preferred securities, and equity securities traded in inactive markets generally are categorized in Level 2 of the fair value hierarchy.

Debt securities generally are traded in the OTC market and are valued at prices furnished by dealers who make markets in such securities or by an independent pricing service, which considers the yield or price of bonds of comparable quality, coupon, maturity, and type, as well as prices quoted by dealers who make markets in such securities. Generally, debt securities are categorized in Level 2 of the fair value hierarchy; however, to the extent the valuations include significant unobservable inputs, the securities would be categorized in Level 3.

Investments in mutual funds are valued at the mutual fund’s closing NAV per share on the day of valuation and are categorized in Level 1 of the fair value hierarchy. Financial futures contracts are valued at closing settlement prices and are categorized in Level 1 of the fair value hierarchy. Assets and liabilities other than financial instruments, including short-term receivables and payables, are carried at cost, or estimated realizable value, if less, which approximates fair value.

Thinly traded financial instruments and those for which the above valuation procedures are inappropriate or are deemed not to reflect fair value are stated at fair value as determined in good faith by the Valuation Committee. The objective of any fair value pricing determination is to arrive at a price that could reasonably be expected from a current sale. Financial instruments fair valued by the Valuation Committee are primarily private placements, restricted securities, warrants, rights, and other securities that are not publicly traded.

Subject to oversight by the Board, the Valuation Committee regularly makes good faith judgments to establish and adjust the fair valuations of certain securities as events occur and circumstances warrant. For instance, in determining the fair value of an equity investment with limited market activity, such as a private placement or a thinly traded public company stock, the Valuation Committee considers a variety of factors, which may include, but are not limited to, the issuer’s business prospects, its financial standing and performance, recent investment transactions in the issuer, new rounds of financing, negotiated transactions of significant size between other investors in the company, relevant market valuations of peer companies, strategic events affecting the company, market liquidity for the issuer, and general economic conditions and events. In consultation with the investment and pricing teams, the Valuation Committee will determine an appropriate valuation technique based on available information, which may include both observable and unobservable inputs. The Valuation Committee typically will afford greatest weight to actual prices in arm’s length transactions, to the extent they represent orderly transactions between market participants, transaction information can be reliably obtained, and prices are deemed representative of fair value. However, the Valuation Committee may also consider other valuation methods such as market-based valuation multiples; a discount or premium from market value of a similar, freely traded security of the same issuer; or some combination. Fair value determinations are reviewed on a regular basis and updated as information becomes available, including actual purchase and sale transactions of the issue. Because any fair value determination involves a significant amount of judgment, there is a degree of subjectivity inherent in such pricing decisions, and fair value prices determined by the Valuation Committee could differ from those of other market participants. Depending on the relative significance of unobservable inputs, including the valuation technique(s) used, fair valued securities may be categorized in Level 2 or 3 of the fair value hierarchy.

Valuation Inputs The following table summarizes the fund’s financial instruments, based on the inputs used to determine their fair values on June 30, 2018 (for further detail by category, please refer to the accompanying Portfolio of Investments):

There were no material transfers between Levels 1 and 2 during the six months ended June 30, 2018.

During the six months ended June 30, 2018, the fund invested in derivative instruments. As defined by GAAP, a derivative is a financial instrument whose value is derived from an underlying security price, foreign exchange rate, interest rate, index of prices or rates, or other variable; it requires little or no initial investment and permits or requires net settlement. The fund invests in derivatives only if the expected risks and rewards are consistent with its investment objectives, policies, and overall risk profile, as described in its prospectus and Statement of Additional Information. The fund may use derivatives for a variety of purposes, such as seeking to hedge against declines in principal value, increase yield, invest in an asset with greater efficiency and at a lower cost than is possible through direct investment, or to adjust credit exposure. The risks associated with the use of derivatives are different from, and potentially much greater than, the risks associated with investing directly in the instruments on which the derivatives are based. The fund at all times maintains sufficient cash reserves, liquid assets, or other SEC-permitted asset types to cover its settlement obligations under open derivative contracts.

The fund values its derivatives at fair value and recognizes changes in fair value currently in its results of operations. Accordingly, the fund does not follow hedge accounting, even for derivatives employed as economic hedges. Generally, the fund accounts for its derivatives on a gross basis. It does not offset the fair value of derivative liabilities against the fair value of derivative assets on its financial statements, nor does it offset the fair value of derivative instruments against the right to reclaim or obligation to return collateral. As of June 30, 2018, the fund held equity futures with cumulative unrealized loss of $2,883,000; the value reflected on the accompanying Statement of Assets and Liabilities is the related unsettled variation margin.

Additionally, during the six months ended June 30, 2018, the fund recognized $2,742,000 of realized gain on Futures and a $(3,393,000) change in unrealized gain/loss on Futures related to its investments in equity derivatives; such amounts are included on the accompanying Statement of Operations.

Counterparty Risk and Collateral The fund invests in exchange-traded or centrally cleared derivative contracts, such as futures, exchange-traded options, and centrally cleared swaps. Counterparty risk on such derivatives is minimal because the clearinghouse provides protection against counterparty defaults. For futures and centrally cleared swaps, the fund is required to deposit collateral in an amount specified by the clearinghouse and the clearing firm (margin requirement), and the margin requirement must be maintained over the life of the contract. Each clearinghouse and clearing firm, in its sole discretion, may adjust the margin requirements applicable to the fund.

Collateral may be in the form of cash or debt securities issued by the U.S. government or related agencies. Cash posted by the fund is reflected as cash deposits in the accompanying financial statements and generally is restricted from withdrawal by the fund; securities posted by the fund are so noted in the accompanying Portfolio of Investments; both remain in the fund’s assets. While typically not sold in the same manner as equity or fixed income securities, exchange-traded or centrally cleared derivatives may be closed out only on the exchange or clearinghouse where the contracts were traded. This ability is subject to the liquidity of underlying positions. As of June 30, 2018, securities valued at $5,212,000 had been posted by the fund for exchange-traded and/or centrally cleared derivatives.

Futures Contracts The fund is subject to equity price risk in the normal course of pursuing its investment objectives and uses futures contracts to help manage such risk. The fund may enter into futures contracts as an efficient means of maintaining liquidity while being invested in the market, to facilitate trading, or to reduce transaction costs. A futures contract provides for the future sale by one party and purchase by another of a specified amount of a specific underlying financial instrument at an agreed upon price, date, time, and place. The fund currently invests only in exchange-traded futures, which generally are standardized as to maturity date, underlying financial instrument, and other contract terms. Payments are made or received by the fund each day to settle daily fluctuations in the value of the contract (variation margin), which reflect changes in the value of the underlying financial instrument. Variation margin is recorded as unrealized gain or loss until the contract is closed. The value of a futures contract included in net assets is the amount of unsettled variation margin; net variation margin receivable is reflected as an asset and net variation margin payable is reflected as a liability on the accompanying Statement of Assets and Liabilities. Risks related to the use of futures contracts include possible illiquidity of the futures markets, contract prices that can be highly volatile and imperfectly correlated to movements in hedged security values, and potential losses in excess of the fund’s initial investment. During the six months ended June 30, 2018, the volume of the fund’s activity in futures, based on underlying notional amounts, was generally less than 1% of net assets.

Consistent with its investment objective, the fund engages in the following practices to manage exposure to certain risks and/or to enhance performance. The investment objective, policies, program, and risk factors of the fund are described more fully in the fund’s prospectus and Statement of Additional Information.

Securities Lending The fund may lend its securities to approved borrowers to earn additional income. Its securities lending activities are administered by a lending agent in accordance with a securities lending agreement. Security loans generally do not have stated maturity dates, and the fund may recall a security at any time. The fund receives collateral in the form of cash or U.S. government securities, valued at 102% to 105% of the value of the securities on loan. Collateral is maintained over the life of the loan in an amount not less than the value of loaned securities; any additional collateral required due to changes in security values is delivered to the fund the next business day. Cash collateral is invested in accordance with investment guidelines approved by fund management. Additionally, the lending agent indemnifies the fund against losses resulting from borrower default. Although risk is mitigated by the collateral and indemnification, the fund could experience a delay in recovering its securities and a possible loss of income or value if the borrower fails to return the securities, collateral investments decline in value, and the lending agent fails to perform. Securities lending revenue consists of earnings on invested collateral and borrowing fees, net of any rebates to the borrower, compensation to the lending agent, and other administrative costs. In accordance with GAAP, investments made with cash collateral are reflected in the accompanying financial statements, but collateral received in the form of securities is not. At June 30, 2018, the value of loaned securities was $457,860,000; the value of cash collateral and related investments was $471,654,000.

Other Purchases and sales of portfolio securities other than short-term securities aggregated $754,036,000 and $2,444,720,000, respectively, for the six months ended June 30, 2018.

No provision for federal income taxes is required since the fund intends to continue to qualify as a regulated investment company under Subchapter M of the Internal Revenue Code and distribute to shareholders all of its taxable income and gains. Distributions determined in accordance with federal income tax regulations may differ in amount or character from net investment income and realized gains for financial reporting purposes. Financial reporting records are adjusted for permanent book/tax differences to reflect tax character but are not adjusted for temporary differences. The amount and character of tax-basis distributions and composition of net assets are finalized at fiscal year-end; accordingly, tax-basis balances have not been determined as of the date of this report.

At June 30, 2018, the cost of investments for federal income tax purposes was $14,426,695,000. Net unrealized gain aggregated $13,816,293,000 at period-end, of which $14,647,075,000 related to appreciated investments and $830,782,000 related to depreciated investments.

The fund is managed by T. Rowe Price Associates, Inc. (Price Associates), a wholly owned subsidiary of T. Rowe Price Group, Inc. (Price Group). The investment management agreement between the fund and Price Associates provides for an annual investment management fee equal to 0.06% of the fund’s average daily net assets. The fee is computed daily and paid monthly.

The Investor Class is subject to a contractual expense limitation through April 30, 2020. During the limitation period, Price Associates is required to waive its management fee or pay any expenses (excluding interest, expenses related to borrowings, taxes, brokerage, and other non-recurring expenses permitted by the investment management agreement) that would otherwise cause the class’s ratio of annualized total expenses to average net assets (expense ratio) to exceed its expense limitation of 0.21%. The class is required to repay Price Associates for expenses previously waived/paid to the extent the class’s net assets grow or expenses decline sufficiently to allow repayment without causing the class’s expense ratio (after the repayment is taken into account) to exceed both: (1) the expense limitation in place at the time such amounts were waived; and (2) the class’s current expense limitation. However, no repayment will be made more than three years after the date of a payment or waiver. For the six months ended June 30, 2018, the Investor Class operated below its expense limitation.

The I Class is also subject to an operating expense limitation (I Class limit) pursuant to which Price Associates is contractually required to pay all operating expenses of the I Class, excluding management fees, interest, expenses related to borrowings, taxes, brokerage, and other non-recurring expenses permitted by the investment management agreement, to the extent such operating expenses, on an annualized basis, exceed 0.05% of average net assets. This agreement will continue until April 30, 2020, and may be renewed, revised, or revoked only with approval of the fund’s Board. The I Class is required to repay Price Associates for expenses previously paid to the extent the class’s net assets grow or expenses decline sufficiently to allow repayment without causing the class’s operating expenses (after the repayment is taken into account) to exceed both: (1) the expense limitation in place at the time such amounts were paid; and (2) the class’s current expense limitation. However, no repayment will be made more than three years after the date of a payment or waiver.

Pursuant to these agreements $487,000 of expenses were repaid to Price Associates during the six months ended June 30, 2018. Including this amount, expenses previously waived/paid by Price Associates in the amount of $2,152,000 remain subject to repayment by the fund at June 30, 2018.

In addition, the fund has entered into service agreements with Price Associates and two wholly owned subsidiaries of Price Associates, each an affiliate of the fund (collectively, Price). Price Associates provides certain accounting and administrative services to the fund. T. Rowe Price Services, Inc., provides shareholder and administrative services in its capacity as the fund’s transfer and dividend-disbursing agent. T. Rowe Price Retirement Plan Services, Inc., provides subaccounting and recordkeeping services for certain retirement accounts invested in the Investor Class and I Class. For the six months ended June 30, 2018, expenses incurred pursuant to these service agreements were $46,000 for Price Associates; $1,435,000 for T. Rowe Price Services, Inc.; and $846,000 for T. Rowe Price Retirement Plan Services, Inc. All amounts due to and due from Price, exclusive of investment management fees payable, are presented net on the accompanying Statement of Assets and Liabilities.

Additionally, the fund is one of several mutual funds in which certain college savings plans managed by Price Associates may invest. As approved by the fund’s Board of Directors, shareholder servicing costs associated with each college savings plan are borne by the fund in proportion to the average daily value of its shares owned by the college savings plan. For the six months ended June 30, 2018, the fund was charged $1,738,000 for shareholder servicing costs related to the college savings plans, of which $1,408,000 was for services provided by Price. All amounts due to and due from Price, exclusive of investment management fees payable, are presented net on the Statement of Assets and Liabilities. At June 30, 2018, approximately 7% of the outstanding shares of the Investor Class were held by college savings plans.

The fund is also one of several mutual funds sponsored by Price Associates (underlying Price funds) in which the T. Rowe Price Retirement Funds (Retirement Funds) may invest. The Retirement Funds do not invest in the underlying Price funds for the purpose of exercising management or control. Pursuant to a special servicing agreement, expenses associated with the operation of the Retirement Funds are borne by each underlying Price fund to the extent of estimated savings to it and in proportion to the average daily value of its shares owned by the Retirement Funds. Expenses allocated under this special servicing agreement are reflected as shareholder servicing expense in the accompanying financial statements. For the six months ended June 30, 2018, the fund was allocated $12,132,000 of Retirement Funds’ expenses. Of these amounts, $3,726,000 related to services provided by Price. All amounts due to and due from Price, exclusive of investment management fees payable, are presented net on the accompanying Statement of Assets and Liabilities. At June 30, 2018, approximately 65% of the outstanding shares of the Investor Class were held by the Retirement Funds.

In addition, other mutual funds, trusts, and other accounts managed by Price Associates or its affiliates (collectively, Price funds and accounts) may invest in the fund and are not subject to a special servicing agreement disclosed above. No Price fund or account may invest for the purpose of exercising management or control over the fund. At June 30, 2018, approximately 88% of the I Class’s outstanding shares were held by Price funds and accounts.

Consistent with its investment objective, the fund may invest in T. Rowe Price Group, Inc. Additionally, the fund may invest its cash reserves in certain open-end management investment companies managed by Price Associates and considered affiliates of the fund: the T. Rowe Price Government Reserve Fund or the T. Rowe Price Treasury Reserve Fund, organized as money market funds, or the T. Rowe Price Short-Term Fund, a short-term bond fund (collectively, the Price Reserve Funds). The Price Reserve Funds are offered as short-term investment options to mutual funds, trusts, and other accounts managed by Price Associates or its affiliates and are not available for direct purchase by members of the public. Cash collateral from securities lending is invested in the T. Rowe Price Short-Term Fund. The Price Reserve Funds pay no investment management fees.

The fund may participate in securities purchase and sale transactions with other funds or accounts advised by Price Associates (cross trades), in accordance with procedures adopted by the fund’s Board and Securities and Exchange Commission rules, which require, among other things, that such purchase and sale cross trades be effected at the independent current market price of the security. During the six months ended June 30, 2018, the fund had no purchases or sales cross trades with other funds or accounts advised by Price Associates.

A description of the policies and procedures used by T. Rowe Price funds and portfolios to determine how to vote proxies relating to portfolio securities is available in each fund’s Statement of Additional Information. You may request this document by calling 1-800-225-5132 or by accessing the SEC’s website, sec.gov.

The description of our proxy voting policies and procedures is also available on our corporate website. To access it, please visit the following Web page:

Scroll down to the section near the bottom of the page that says, “Proxy Voting Policies.” Click on the Proxy Voting Policies link in the shaded box.

Each fund’s most recent annual proxy voting record is available on our website and through the SEC’s website. To access it through T. Rowe Price, visit the website location shown above, and scroll down to the section near the bottom of the page that says, “Proxy Voting Records.” Click on the Proxy Voting Records link in the shaded box.

The fund files a complete schedule of portfolio holdings with the Securities and Exchange Commission for the first and third quarters of each fiscal year on Form N-Q. The fund’s Form N-Q is available electronically on the SEC’s website (sec.gov); hard copies may be reviewed and copied at the SEC’s Public Reference Room, 100 F St. N.E., Washington, DC 20549. For more information on the Public Reference Room, call 1-800-SEC-0330.

Each year, the fund’s Board of Directors (Board) considers the continuation of the investment management agreement (Advisory Contract) between the fund and its investment advisor, T. Rowe Price Associates, Inc. (Advisor), on behalf of the fund. In that regard, at an in-person meeting held on March 5–6, 2018 (Meeting), the Board, including a majority of the fund’s independent directors, approved the continuation of the fund’s Advisory Contract. At the Meeting, the Board considered the factors and reached the conclusions described below relating to the selection of the Advisor and the approval of the Advisory Contract. The independent directors were assisted in their evaluation of the Advisory Contract by independent legal counsel from whom they received separate legal advice and with whom they met separately.

In providing information to the Board, the Advisor was guided by a detailed set of requests for information submitted by independent legal counsel on behalf of the independent directors. In considering and approving the Advisory Contract, the Board considered the information it believed was relevant, including, but not limited to, the information discussed below. The Board considered not only the specific information presented in connection with the Meeting but also the knowledge gained over time through interaction with the Advisor about various topics. The Board meets regularly and, at each of its meetings, covers an extensive agenda of topics and materials and considers factors that are relevant to its annual consideration of the renewal of the T. Rowe Price funds’ advisory contracts, including performance and the services and support provided to the funds and their shareholders.

Services Provided by the Advisor
The Board considered the nature, quality, and extent of the services provided to the fund by the Advisor. These services included, but were not limited to, directing the fund’s investments in accordance with its investment program and the overall management of the fund’s portfolio, as well as a variety of related activities such as financial, investment operations, and administrative services; compliance; maintaining the fund’s records and registrations; and shareholder communications. The Board also reviewed the background and experience of the Advisor’s senior management team and investment personnel involved in the management of the fund, as well as the Advisor’s compliance record. The Board concluded that it was satisfied with the nature, quality, and extent of the services provided by the Advisor.

Investment Performance of the Fund
The Board took into account discussions with the Advisor and reports that it receives throughout the year relating to fund performance. In connection with the Meeting, the Board reviewed the fund’s net annualized total returns for the 1-, 2-, 3-, 4-, 5-, and 10-year periods as of September 30, 2017, and compared these returns with the performance of a peer group of funds with similar investment programs and a wide variety of other previously agreed-upon comparable performance measures and market data, including those supplied by Broadridge, which is an independent provider of mutual fund data.

On the basis of this evaluation and the Board’s ongoing review of investment results, and factoring in the relative market conditions during certain of the performance periods, the Board concluded that the fund’s performance was satisfactory.

Costs, Benefits, Profits, and Economies of Scale
The Board reviewed detailed information regarding the revenues received by the Advisor under the Advisory Contract and other benefits that the Advisor (and its affiliates) may have realized from its relationship with the fund, including any research received under “soft dollar” agreements and commission-sharing arrangements with broker-dealers. The Board considered that the Advisor may receive some benefit from soft-dollar arrangements pursuant to which research is received from broker-dealers that execute the fund’s portfolio transactions. The Board received information on the estimated costs incurred and profits realized by the Advisor from managing the T. Rowe Price funds. The Board also reviewed estimates of the profits realized from managing the fund in particular, and the Board concluded that the Advisor’s profits were reasonable in light of the services provided to the fund.

The Board also considered whether the fund benefits under the fee levels set forth in the Advisory Contract from any economies of scale realized by the Advisor. Under the Advisory Contract, the fund pays a fee to the Advisor for investment management services based on the fund’s average daily net assets and the fund pays its own expenses of operations (subject to an expense limitation on total expense ratio with respect to the Investor Class and an expense limitation on operating expenses with respect to the I Class). Effective August 1, 2017, the fund’s management fee was reduced from 0.10% to 0.06%. The fund’s shareholders have benefitted from potential economies of scale through reductions to the fund’s contractual management fee rate and expense limitations over the past several years. The Board concluded that the advisory fee structure continued to be appropriate.

Fees and Expenses
The Board was provided with information regarding industry trends in management fees and expenses. Among other things, the Board reviewed data for peer groups that were compiled by Broadridge, which compared: (i) contractual management fees, total expenses, actual management fees, and nonmanagement expenses of the fund with a group of competitor funds selected by Broadridge (Expense Group); and (ii) total expenses, actual management fees, and nonmanagement expenses of the fund with a broader set of funds within the Lipper investment classification (Expense Universe). The Board considered the fund’s contractual management fee rate, actual management fee rate (which reflects the management fees actually received from the fund by the Advisor after any applicable waivers, reductions, or reimbursements), operating expenses, and total expenses (which reflect the net total expense ratio of the fund after any waivers, reductions, or reimbursements) in comparison with the information for the Broadridge peer groups. Broadridge generally constructed the peer groups by seeking the most comparable funds based on similar investment classifications and objectives, expense structure, asset size, and operating components and attributes and ranked funds into quintiles, with the first quintile representing the funds with the lowest relative expenses and the fifth quintile representing the funds with the highest relative expenses. The information provided to the Board indicated that the fund’s contractual management fee ranked in the second quintile (Expense Group), the fund’s actual management fee rate ranked in the first quintile (Expense Group and Expense Universe), and the fund’s total expenses ranked in the second and fourth quintiles (Expense Group) and first and second quintiles (Expense Universe).

The Board also reviewed the fee schedules for institutional accounts and private accounts with similar mandates that are advised or subadvised by the Advisor and its affiliates. Management provided the Board with information about the Advisor’s responsibilities and services provided to subadvisory and other institutional account clients, including information about how the requirements and economics of the institutional business are fundamentally different from those of the mutual fund business. The Board considered information showing that the Advisor’s mutual fund business is generally more complex from a business and compliance perspective than its institutional account business and considered various relevant factors, such as the broader scope of operations and oversight, more extensive shareholder communication infrastructure, greater asset flows, heightened business risks, and differences in applicable laws and regulations associated with the Advisor’s proprietary mutual fund business. In assessing the reasonableness of the fund’s management fee rate, the Board considered the differences in the nature of the services required for the Advisor to manage its mutual fund business versus managing a discrete pool of assets as a subadvisor to another institution’s mutual fund or for an institutional account, and that the Advisor generally performs significant additional services and assumes greater risk in managing the fund and other T. Rowe Price funds than it does for institutional account clients.

On the basis of the information provided and the factors considered, the Board concluded that the fees paid by the fund under the Advisory Contract are reasonable.

Approval of the Advisory Contract
As noted, the Board approved the continuation of the Advisory Contract. No single factor was considered in isolation or to be determinative to the decision. Rather, the Board concluded, in light of a weighting and balancing of all factors considered, that it was in the best interests of the fund and its shareholders for the Board to approve the continuation of the Advisory Contract (including the fees to be charged for services thereunder).

A code of ethics, as defined in Item 2 of Form N-CSR, applicable to its principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions is filed as an exhibit to the registrant’s annual Form N-CSR. No substantive amendments were approved or waivers were granted to this code of ethics during the registrant’s most recent fiscal half-year.

(a) Not applicable. The complete schedule of investments is included in Item 1 of this Form N-CSR.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies.

Item 9. Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers.

(a) The registrant’s principal executive officer and principal financial officer have evaluated the registrant’s disclosure controls and procedures within 90 days of this filing and have concluded that the registrant’s disclosure controls and procedures were effective, as of that date, in ensuring that information required to be disclosed by the registrant in this Form N-CSR was recorded, processed, summarized, and reported timely.

(b) During the period, the Price Funds’ accounting agent, The Bank of New York Mellon (BNYM), converted the fund’s books and records from a legacy fund accounting system / operating model to a BNYM fund accounting system / operating model.

(a)(1) The registrant’s code of ethics pursuant to Item 2 of Form N-CSR is filed with the registrant’s annual Form N-CSR.

(2) Separate certifications by the registrant's principal executive officer and principal financial officer, pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 and required by Rule 30a-2(a) under the Investment Company Act of 1940, are attached.

(3) Written solicitation to repurchase securities issued by closed-end companies: not applicable.

(b) A certification by the registrant's principal executive officer and principal financial officer, pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 and required by Rule 30a-2(b) under the Investment Company Act of 1940, is attached.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

T. Rowe Price Index Trust, Inc.

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

		By	/s/ David Oestreicher
			David Oestreicher
			Principal Executive Officer

Date	August 16, 2018


		By	/s/ Catherine D. Mathews
			Catherine D. Mathews
			Principal Financial Officer

Date	August 16, 2018

■	The Equity Market Index Funds each tracked their unmanaged benchmarks for the six-month period ended June 30, 2018, and produced positive results.

■	Using full replication and sampling strategies, we kept the composition and other attributes of the portfolios similar to those of their benchmarks.

■	A small number of information technology and consumer discretionary stocks accounted for most of the S&P 500 Stock Index’s advance.

■	In the near term, we acknowledge that strong earnings growth could continue to buttress stocks, and we believe that equities gains could be fueled by a narrow list of winning stocks.

/s/ David Oestreicher

David Oestreicher

Principal Executive Officer

August 16, 2018