What's the difference between prime and government money market funds?

US money market funds held roughly $7.9 trillion as of October 2026, according to data from the Investment Company Institute. Many corporate treasury teams use more than one fund. Prime and government are formal fund categories under SEC rules, but the labels alone don't show how differently the two types behave. The core distinction is between funds that lend almost entirely to the US government and those that also lend to banks and other companies.

This guide shows how prime and government money market funds differ in what they hold, how they are priced, and how they act under stress. It also covers the SEC's most recent reforms and what these choices mean for your investment policy.

Prime and government funds at a glance

A money market fund pools investor cash into short-term debt, as our guide to money market funds explains. Prime and government funds share that structure, but each takes on a different kind of credit exposure.

What a government money market fund holds

According to SEC Rule 2a-7 regulations, a government money market fund must invest at least 99.5% of its total assets in cash, government securities, and repurchase agreements fully collateralized by government securities. In practice, this means US Treasury bills, short-term Treasury notes, debt issued by federal agencies, and reverse repo secured by Treasury and agency collateral. Some government funds go further and restrict their holdings to Treasury securities and repo backed by them. A fund's credit exposure is to the US government, its agencies, or repo counterparties whose obligations are backed by government collateral.

What a prime money market fund holds

A prime fund can also buy short-term debt from banks and companies, such as certificates of deposit, commercial paper, and asset-backed commercial paper. Rule 2a-7 limits these holdings to high-quality instruments with short maturities, most of which mature in weeks or months. A prime fund often holds some government debt too, but because banks are the main issuers of CDs and much of the commercial paper market, its credit exposure usually leans heavily toward financial institutions.

How SEC rules classify prime and government funds

US money market funds are governed by Rule 2a-7 under the Investment Company Act of 1940. The rule separates government funds from non-government funds, and then splits non-government funds into retail and institutional categories. That second split determines which prime funds a corporate treasury can actually use.

Government funds

Government funds can use amortized cost valuation, valuing holdings at purchase price plus the interest they are set to earn, to seek a stable share price of $1.00. They’re open to both retail and institutional investors. Government funds are not required to impose liquidity fees on redemptions, although a fund's board can reserve the right to introduce them.

Retail prime funds

Retail money market funds are generally limited to natural persons. They can also seek a stable $1.00 share price. Because corporations, partnerships, and funds are not natural persons, retail prime funds are generally outside the investable universe for corporate treasury cash.

Institutional prime funds

Institutional prime funds are the route to a prime strategy for corporate investors. They must price their shares at a floating net asset value based on the current market value of their holdings, typically calculated to four decimal places. Each redemption can therefore realize a small gain or loss, which treasury and accounting teams need to track.

Institutional prime funds also carry a mandatory liquidity fee. Since October 2, 2024, these funds must impose a fee when daily net redemptions exceed 5% of net assets, unless the fund's liquidity costs are de minimis. Their boards can also impose discretionary liquidity fees when they judge a fee to be in the fund's best interest.

The difference in scale is significant. For the week ended October 21, 2026, institutional government funds held $4.56 trillion, while institutional prime funds held about $252 billion, according to the Investment Company Institute. Treasurers who want prime exposure therefore have a much narrower pool of funds to choose from.

Tax-exempt or municipal money market funds form a third category, also split into retail and institutional versions. They are designed mainly for investors with US tax considerations and sit outside the scope of this guide.

How prime and government funds compare

Credit risk and diversification

A government fund's risk is tied closely to the creditworthiness of the US government. A prime fund spreads its risk across many banks and companies, but banks commonly come under pressure at the same time during a financial crisis. Our article on why diversification matters for corporate cash explains how these linked risks can affect a portfolio.

Yield

Prime funds usually pay a higher yield than government funds, reflecting the credit spread over government benchmarks on bank and corporate paper. Both types track the federal funds rate closely, since their holdings are short-term and reprice as they mature. The gap moves with conditions in bank funding markets, so treasurers should compare seven-day SEC yields, quoted net of fund expenses.

Liquidity rules and redemption pressure

Since April 2, 2024, every money market fund must hold at least 25% of its total assets in daily liquid assets and 50% in weekly liquid assets, up from 10% and 30% previously. The SEC also removed funds' ability to suspend redemptions through gates.

Both fund types follow the same liquidity minimums, but their assets behave differently under stress. Treasury bills generally remain easy to sell in a crisis, while certificates of deposit and commercial paper can become hard to trade. Our guide to managing liquidity risk explains how treasurers can plan for this difference.

How prime funds behaved in March 2020

The dash for cash in March 2020 showed how the two fund types behave when markets freeze. Prime money market funds had outflows of $139 billion that month, equal to 17.6% of their net assets at the end of February, according to the Investment Company Institute. The Federal Reserve set up the Money Market Mutual Fund Liquidity Facility to help prime funds meet redemptions.

The pattern of outflows mattered as much as their size. ICI analysis found that outflows were much stronger from institutional prime funds whose weekly liquid assets had fallen to 35% or below, even though those funds were still above the 30% regulatory minimum at the time. Investors appear to have redeemed early to avoid fees or gates, a dynamic that shaped the SEC's next round of reform.

SEC money market fund reform

The SEC adopted its latest money market fund amendments on July 12, 2023. The changes removed redemption gates and broke the link between weekly liquid asset levels and liquidity fees, raised the daily and weekly liquidity minimums, and introduced the mandatory liquidity fee for institutional prime and institutional tax-exempt funds. The final compliance date passed on October 2, 2024, so the framework now applies in full.

For treasurers, the reforms make government and institutional prime funds more distinct than before. Government funds keep a stable share price and have no mandatory fee. Institutional prime funds combine a floating share price with a fee that can apply on heavy redemption days, which is exactly when treasury teams are most likely to need their cash.

Choosing between prime and government funds

The right mix depends on what each pool of cash is for and the limits in your investment policy. Some treasury teams keep operating cash that must stay available during a crisis in government funds. Others accept bank credit risk in institutional prime funds for balances they hold as a longer-term buffer.

Treasury policies at large companies and multinationals, and reserves policies at nonprofits and foundations, often set separate limits for government and bank exposure.

Direct government and bank exposure without pooling

Both prime and government funds pool investor cash and use some maturity transformation, offering daily access even though holdings mature over weeks or months. This structure means each investor is affected by other investors' redemption decisions.

TreasurySpring's Fixed-Term Funds are designed to give segregated exposure to a single issuer for a set term. Treasurers can choose government exposure, such as US Treasury bills, or exposure to investment-grade banks, either unsecured or secured through tri-party and centrally cleared repo. Each Fixed-Term Fund is structured to match the maturity of its underlying instrument, so there is no maturity transformation and no commingling with other investors.

The trade-off is that cash is committed for the chosen term rather than available on demand. Some treasurers use Fixed-Term Funds alongside money market funds, keeping daily liquidity in funds and placing core balances directly. Our platform offers a range of options across government, bank, and corporate counterparties with terms as short as one day.

Pairing the fund to the purpose of the cash

Government and prime money market funds share the same basic structure but carry different credit exposure. SEC rules sharpen that split: government funds offer a stable share price and no mandatory fees, while institutional prime funds float their price and must charge fees on heavy redemption days. Prime funds have historically paid more because of bank credit risk and less-liquid assets, while government funds accept lower yields for greater resilience under stress.

With the 2023 reforms now fully in effect, this is a good time to review which funds your policy allows and why. If you would like to compare your fund allocation with direct, segregated exposure to governments and banks, contact our team. We can talk you through the options and how they fit alongside your existing holdings.

For anyone who can't tell the difference between their SEC and their ASC, we've introduced our Treasury & Cash Investment Glossary.

*TreasurySpring’s blogs and commentaries are provided for general information purposes only, and do not constitute legal, investment or other advice.