497

Prospectus Supplement	February 28, 2017
Putnam Money Market Fund Prospectus dated January 30, 2017

Effective April 1, 2017, purchases of class B shares will be closed to new and existing investors except by exchange from class B shares of another Putnam fund or through dividend and/or capital gains reinvestment.

The fund’s Board of Trustees has determined to limit payments under the distribution and service (12b-1) plans in place with respect to class B, class C, class M, class R and class T1 shares to 0.00% of average net assets effective as of the close of business on March 31, 2017. Beginning on April 1, 2017, the fund will no longer make payments under the distribution and service (12b-1) plans in place with respect to class B, class C, class M, class R and class T1 shares.

The following information replaces similar disclosure for the fund under Fees and expenses:

The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. Information about sales charge discounts is available from your financial advisor and in the Appendix to the fund’s prospectus.

The following information replaces similar disclosure for the fund under Fees and expenses:

Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Share class	Management fees	Other expenses =	Total annual fund operating expenses
Class A	0.28%	0.23%	0.51%
Class B	0.28%	0.23%	0.51%
Class C	0.28%	0.23%	0.51%
Class M	0.28%	0.23%	0.51%
Class R	0.28%	0.23%	0.51%
Class T1	0.28%	0.23%	0.51%

* A deferred sales charge on class A, B, C, and T1 shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.

= Restated to reflect current fees resulting from a change to the fund’s investor servicing arrangements effective September 1, 2016.

Example

The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.

Share class	1 year	3 years	5 years	10 years
Class A	$52	$164	$285	$640
Class B*	$552	$464	$485	$640
Class B (no redemptions)	$52	$164	$285	$640
Class C	$52	$164	$285	$640
Class M	$52	$164	$285	$640
Class R	$52	$164	$285	$640
Class T1	$52	$164	$285	$640

* Reflects assessment of deferred sales charge assuming Class B shares were acquired by exchange from one or more other Putnam funds immediately after purchase of shares from such other fund(s).

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Putnam Money Market Fund Supplement

Total

Risk/Return:

Supplement Text

Prospectus Supplement	February 28, 2017
Putnam Money Market Fund Prospectus dated January 30, 2017

Effective April 1, 2017, purchases of class B shares will be closed to new and existing investors except by exchange from class B shares of another Putnam fund or through dividend and/or capital gains reinvestment.

The fund’s Board of Trustees has determined to limit payments under the distribution and service (12b-1) plans in place with respect to class B, class C, class M, class R and class T1 shares to 0.00% of average net assets effective as of the close of business on March 31, 2017. Beginning on April 1, 2017, the fund will no longer make payments under the distribution and service (12b-1) plans in place with respect to class B, class C, class M, class R and class T1 shares.

The following information replaces similar disclosure for the fund under Fees and expenses:

The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. Information about sales charge discounts is available from your financial advisor and in the Appendix to the fund’s prospectus.

The following information replaces similar disclosure for the fund under Fees and expenses:

Annual fund operating expenses
(expenses you pay each year as a percentage of the value of your investment)
Share class	Management fees	Other expenses =	Total annual fund operating expenses
Class A	0.28%	0.23%	0.51%
Class B	0.28%	0.23%	0.51%
Class C	0.28%	0.23%	0.51%
Class M	0.28%	0.23%	0.51%
Class R	0.28%	0.23%	0.51%
Class T1	0.28%	0.23%	0.51%

* A deferred sales charge on class A, B, C, and T1 shares may apply to certain redemptions of shares purchased by exchange from another Putnam fund. The rate of the deferred sales charge for Class B shares will be determined based on the time between the original purchase of Class B shares from the other Putnam fund(s) and the date of redemption of shares from this fund.

= Restated to reflect current fees resulting from a change to the fund’s investor servicing arrangements effective September 1, 2016.

Example

The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.

Share class	1 year	3 years	5 years	10 years
Class A	$52	$164	$285	$640
Class B*	$552	$464	$485	$640
Class B (no redemptions)	$52	$164	$285	$640
Class C	$52	$164	$285	$640
Class M	$52	$164	$285	$640
Class R	$52	$164	$285	$640
Class T1	$52	$164	$285	$640

* Reflects assessment of deferred sales charge assuming Class B shares were acquired by exchange from one or more other Putnam funds immediately after purchase of shares from such other fund(s).

XML

Putnam Money Market Fund

Fees and expenses

The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. Information about sales charge discounts is available from your financial advisor and in the Appendix to the fund’s prospectus.

Annual fund operating expenses (expenses you pay each year as a percentage of the value of your investment)

Annual Fund Operating Expenses - Putnam Money Market Fund		Class A	Class B	Class C	Class M	Class R	Class T
Management fees		0.28%	0.28%	0.28%	0.28%	0.28%	0.28%
Other expenses	[1]	0.23%	0.23%	0.23%	0.23%	0.23%	0.23%
Total annual fund operating expenses		0.51%	0.51%	0.51%	0.51%	0.51%	0.51%

Example

The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.

Expense Example - Putnam Money Market Fund - USD ($)		Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
Class A		52	164	285	640
Class B	[1]	552	464	485	640
Class C		52	164	285	640
Class M		52	164	285	640
Class R		52	164	285	640
Class T		52	164	285	640

Expense Example, No Redemption	Expense Example, No Redemption, 1 Year	Expense Example, No Redemption, 3 Years	Expense Example, No Redemption, 5 Years	Expense Example, No Redemption, 10 Years
Putnam Money Market Fund | Class B | USD ($)	52	164	285	640

[1] Restated to reflect current fees resulting from a change to the fund's investor servicing arrangements effective September 1, 2016.

[1] Reflects assessment of deferred sales charge assuming Class B shares were acquired by exchange from one or more other Putnam funds immediately after purchase of shares from such other fund(s).

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Feb. 28, 2017
Registrant Name	dei_EntityRegistrantName	PUTNAM MONEY MARKET FUND
Central Index Key	dei_EntityCentralIndexKey	0000081248
Amendment Flag	dei_AmendmentFlag	false
Trading Symbol	dei_TradingSymbol	PDDXX
Document Creation Date	dei_DocumentCreationDate	Mar. 10, 2017
Document Effective Date	dei_DocumentEffectiveDate	Apr. 01, 2017
Prospectus Date	rr_ProspectusDate	Jan. 30, 2017
Putnam Money Market Fund
Risk/Return:	rr_RiskReturnAbstract
Expense [Heading]	rr_ExpenseHeading	Fees and expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. Information about sales charge discounts is available from your financial advisor and in the Appendix to the fund’s prospectus.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual fund operating expenses (expenses you pay each year as a percentage of the value of your investment)
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then redeem or hold all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same. Your actual costs may be higher or lower.
Putnam Money Market Fund | Class A
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class B
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 552	[2]
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	464	[2]
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	485	[2]
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	640	[2]
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	52
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	164
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	285
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	$ 640
Putnam Money Market Fund | Class C
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class M
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class R
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640
Putnam Money Market Fund | Class T
Risk/Return:	rr_RiskReturnAbstract
Management fees	rr_ManagementFeesOverAssets	0.28%
Other expenses	rr_OtherExpensesOverAssets	0.23%	[1]
Total annual fund operating expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 640

[1] Restated to reflect current fees resulting from a change to the fund's investor servicing arrangements effective September 1, 2016.

[2] Reflects assessment of deferred sales charge assuming Class B shares were acquired by exchange from one or more other Putnam funds immediately after purchase of shares from such other fund(s).