[JANUS HENDERSON LOGO]

Janus Henderson U.S. Managed Volatility Fund

Ticker: JRSDX Class D Shares*

* Effective July 6, 2020, Class D Shares are open to new investors. Until that time, Class D Shares remain closed to new investors, with certain limited exceptions.

Summary Prospectus dated October 28, 2019
As Supplemented June 19, 2020

Before you invest, you may want to review the Fund’s Prospectus, which contains more information about the Fund and its risks. You can find the Fund’s Prospectus, reports to shareholders, and other information about the Fund online at janushenderson.com/reports. You can also get this information at no cost by calling a Janus Henderson representative at 1-800-525-3713 or by sending an email request to prospectusorder@janushenderson.com.

Beginning on January 1, 2021, as permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the Fund’s shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the reports from the Fund or your plan sponsor, broker-dealer, or financial intermediary, or if you invest directly with the Fund, by contacting a Janus Henderson representative. Instead, the reports will be made available on a website, and you will be notified by mail each time a report is posted and provided with a website link to access the report.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications from the Fund electronically by contacting your plan sponsor, broker-dealer, or financial intermediary, or if you invest directly with the Fund, by visiting janushenderson.com/edelivery.

You may elect to receive all future reports in paper free of charge. If you do not invest directly with the Fund, you should contact your plan sponsor, broker-dealer, or financial intermediary, to request to continue receiving paper copies of your shareholder reports. If you invest directly with the Fund, you can call 1-800-525-3713 to let the Fund know that you wish to continue receiving paper copies of your shareholder reports. Your election to receive reports in paper will apply to all Janus Henderson mutual funds where held (i.e., all Janus Henderson mutual funds held in your account if you invest through your financial intermediary or all Janus Henderson mutual funds held with the fund complex if you invest directly with a fund).

Investment Objective

Janus Henderson U.S. Managed Volatility Fund seeks long-term growth of capital.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold Shares of the Fund.

ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)	Class D
Management Fees	0.50%
Other Expenses	0.21%
Total Annual Fund Operating Expenses	0.71%

EXAMPLE:

The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated, reinvest all dividends and distributions, and then redeem all of your Shares at the end of each period. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	1 Year	3 Years	5 Years	10 Years
Class D Shares	$ 73	$ 227	$ 395	$ 883

Portfolio Turnover: The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 87% of the average value of its portfolio.

1  Janus Henderson U.S. Managed Volatility Fund

Principal investment strategies

The Fund invests, under normal circumstances, at least 80% of its net assets (plus any borrowings for investment purposes) in U.S. common stocks from the universe of the Russell 1000^® Index, utilizing Intech Investment Management LLC’s (“Intech”) mathematical investment process, applying a managed volatility approach. The Russell 1000^® Index is an unmanaged index that measures the performance of the large-cap segment of the U.S. equity universe. The Fund seeks to produce returns in excess of the Russell 1000^® Index (the Fund’s benchmark index), but with lower absolute volatility than the benchmark index. The Fund seeks to generate such excess returns with absolute volatility that can range from approximately 0% to 40% lower than the Russell 1000^® Index. In this context, absolute volatility refers to the variation in the returns of the Fund and the benchmark index as measured by the standard deviation of monthly returns. This range is expected to be closer to 0% in less volatile markets and will increase as market conditions become more volatile. The Fund transitioned to a managed volatility strategy in December 2014. Since January 2015, when seeking to generate returns, the Fund has reduced volatility on average by approximately 18% relative to its named benchmark index (based on the standard deviation of monthly returns). As noted, the volatility reduction is expected to vary over time based on market conditions and other factors.

The Fund pursues its investment objective by applying a mathematical investment process to construct an investment portfolio from the universe of stocks within the named benchmark index. The goal of this process is to combine stocks that individually have higher relative volatility, lower absolute volatility, and lower correlations with each other in an effort to reduce the Fund’s absolute volatility, while still generating returns that exceed the named benchmark index over a full market cycle (a time period representing a significant market decline and recovery). Although the Fund is generally expected to underperform its named benchmark index in sharply rising markets, this strategy seeks to participate in normal rising markets and lessen losses in down markets. In applying this strategy, Intech establishes target proportions of its holdings from stocks within the named benchmark index using an optimization process designed to determine the most effective weightings of each stock in the Fund. Once Intech determines such proportions and the Fund’s investments are selected, the Fund is periodically rebalanced to the set target proportions and re-optimized. The rebalancing techniques used by Intech may result in a higher relative portfolio turnover rate compared to a “buy and hold” fund strategy.

The Fund may lend portfolio securities on a short-term or long-term basis, in an amount equal to up to one-third of its total assets as determined at the time of the loan origination.

Principal investment risks

The biggest risk is that the Fund’s returns will vary, and you could lose money. The Fund is designed for long-term investors seeking an equity portfolio, including common stocks. Common stocks tend to be more volatile than many other investment choices.

Investment Process Risk.  The focus on managed volatility may keep the Fund from achieving excess returns over the named benchmark index. In this regard, Intech’s managed volatility strategy may underperform the Fund’s named benchmark index during certain periods of up markets, and in particular, most likely will underperform the benchmark index in sharply rising markets, and may not achieve the desired level of protection in down markets. As Intech’s mathematical investment process has evolved, it has experienced periods of both underperformance and outperformance relative to the named benchmark index. Even when the proprietary mathematical investment process is working appropriately, Intech expects that there will be periods of underperformance relative to the benchmark index. On an occasional basis, Intech makes changes to its mathematical investment process that do not require shareholder notice. These changes may result in changes to the portfolio, might not provide the intended results, and may adversely impact the Fund’s performance.

Small- and Mid-Sized Companies Risk.  The Fund’s investments in securities issued by small- and mid-sized companies, which can include smaller, start-up companies offering emerging products or services, may involve greater risks than are customarily associated with larger, more established companies. Securities issued by small- and mid-sized companies tend to be more volatile and somewhat more speculative than securities issued by larger or more established companies and may underperform as compared to the securities of larger or more established companies.

Market Risk.  The value of the Fund’s portfolio may decrease if the value of an individual company or security, or multiple companies or securities, in the portfolio decreases. Further, regardless of how well individual companies or securities perform, the value of the Fund’s portfolio could also decrease if there are deteriorating economic or market conditions. It is important

2  Janus Investment Fund

to understand that the value of your investment may fall, sometimes sharply, in response to changes in the market, and you could lose money. Market risk may affect a single issuer, industry, economic sector, or the market as a whole.

Real Estate Securities Risk.  The Fund’s performance may be affected by the risks associated with investments in real estate-related companies. The value of real estate-related companies’ securities is sensitive to changes in real estate values and rental income, property taxes, interest rates, tax and regulatory requirements, supply and demand, and the management skill and creditworthiness of the company. Investments in real estate investment trusts (“REITs”) involve the same risks as other real estate investments. In addition, a REIT could fail to qualify for tax-free pass-through of its income under the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”) or fail to maintain its exemption from registration under the Investment Company Act of 1940, as amended, which could produce adverse economic consequences for the REIT and its investors, including the Fund.

Portfolio Turnover Risk.  Increased portfolio turnover may result in higher costs, which may offset gains or increase losses in the Fund’s performance. In addition, higher portfolio turnover may result in the acceleration of capital gains and the recognition of greater levels of short-term capital gains, which are taxed at ordinary federal income tax rates when distributed to shareholders.

Securities Lending Risk.  The Fund may seek to earn additional income through lending its securities to certain qualified broker-dealers and institutions. There is the risk that when portfolio securities are lent, the securities may not be returned on a timely basis, and the Fund may experience delays and costs in recovering the security or gaining access to the collateral provided to the Fund to collateralize the loan. If the Fund is unable to recover a security on loan, the Fund may use the collateral to purchase replacement securities in the market. There is a risk that the value of the collateral could decrease below the cost of the replacement security by the time the replacement investment is made, resulting in a loss to the Fund.

An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Performance information

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on December 22, 2014. The performance shown for Class D Shares for the period July 6, 2009 to December 22, 2014, reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. Performance shown for periods prior to July 6, 2009, reflects the historical performance of Janus Adviser INTECH Risk-Managed Value Fund’s (the “JAD predecessor fund”) Class I Shares prior to the reorganization of Class I Shares of the JAD predecessor fund into Class I Shares of the Fund, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to December 22, 2014, the performance shown may have been different. The performance shown for the periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.Updated performance information is available at janushenderson.com/allfunds or by calling 1-800-525-3713.

3  Janus Henderson U.S. Managed Volatility Fund

Annual Total Returns for Class D Shares (calendar year-end)

Best Quarter: 3rd Quarter 2009 17.77% Worst Quarter: 1st Quarter 2009 – 16.68%

The Fund’s year-to-date return as of the calendar quarter ended September 30, 2019 was 20.46%.

Average Annual Total Returns (periods ended 12/31/18)
	1 Year	5 Years	10 Years	Since Inception of Predecessor Fund (12/30/05)
Class D Shares
Return Before Taxes	– 3.60%	7.13%	11.85%	6.86%
Return After Taxes on Distributions	– 5.51%	3.74%	9.29%	4.82%
Return After Taxes on Distributions and Sale of Fund Shares(1)	– 0.95%	4.64%	9.10%	5.01%
Russell 1000® Index (reflects no deduction for expenses, fees, or taxes)	– 4.78%	8.21%	13.28%	7.79%

(1)  If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

The Fund’s primary benchmark index is the Russell 1000^® Index. The index is described below.

• The Russell 1000^® Index measures the performance of the large-cap segment of the U.S. equity universe.

After-tax returns are calculated using distributions for the Fund’s Class D Shares for periods following December 22, 2014; for the Fund’s Class I Shares for the period following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-advantaged account, such as a 401(k) plan or an IRA.

Management

Investment Adviser:  Janus Capital Management LLC

Investment Subadviser:  Intech Investment Management LLC

Portfolio Management:  A team of investment professionals consisting ofAdrian Banner, Ph.D. (Chief Executive Officer since November 2012 and Chief Investment Officer since January 2012),Vassilios Papathanakos, Ph.D. (Deputy Chief Investment Officer since November 2012), andJoseph W. Runnels, CFA (Vice President of Portfolio Management since March 2003) works together to implement the mathematical investment process. No one person of the Fund’s investment team is primarily responsible for implementing the investment strategies of the Fund.

4  Janus Investment Fund

Purchase and sale of Fund shares

Minimum Investment Requirements
To open a new regular Fund account	$2,500
To open a new regular Fund account with an automatic investment program of $50 per month	$ 100
To open a new UGMA/UTMA account, Coverdell Education Savings Account, or a retirement Fund account
• without an automatic investment program	$1,000
• with an automatic investment program of $50 per month	$ 100
To add to any existing type of Fund account without an automatic investment program	$ 50

You may generally purchase, exchange, or redeem Fund Shares on any business day by written request, wire transfer, telephone, and in most cases, online at janushenderson.com/individual. You may conduct transactions by mail (Janus Henderson, P.O. Box 219109, Kansas City, MO 64121-9109), or by telephone at 1-800-525-3713. Purchase, exchange, or redemption requests must be received in good order by the Fund or its agents prior to the close of the regular trading session of the New York Stock Exchange in order to receive that day’s net asset value. For additional information, refer to “To Open an Account or Buy Shares,” “To Exchange Shares,” and/or “To Sell Shares” in the Prospectus.

Tax information

The Fund’s distributions are taxable, and will be taxed as ordinary income or capital gains, unless you are investing through a tax-advantaged arrangement, such as a 401(k) plan or an individual retirement account (in which case you may be taxed upon withdrawal of your investment from such account).

Payments to broker-dealers and other financial intermediaries

With respect to share classes not offered in this Prospectus, the Fund and its related companies pay select broker-dealer firms or other financial intermediaries for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing a broker-dealer or other intermediary or a salesperson to recommend the Fund over another investment or to recommend one share class over another.

5  Janus Henderson U.S. Managed Volatility Fund