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Smartphone showing a flat, stable line chart next to a neat stack of cash, symbolizing the low-volatility, low-risk nature of money market funds. |
This guide explains how money market funds try to stay stable, what "breaking the buck" actually means and how often it's happened, the real difference between a money market fund and a money market deposit account at a bank, and what protection actually applies (and doesn't) if something goes wrong. (If you're weighing this against market risk in a retirement account, our companion piece on whether you can lose money in a Roth IRA covers that side of the equation.)
The Short Answer: Yes, But It's Rare
A money market fund is a type of mutual fund that invests in short-term, high-quality debt like Treasury bills, commercial paper, and repurchase agreements. It aims to keep its share price fixed at $1.00, paying out any earnings as dividends rather than letting the share price rise. If the fund's underlying investments lose enough value, the share price can fall below $1.00 — an event known in the industry as "breaking the buck."
This has happened only a handful of times in the history of money market funds, and regulatory changes since the 2008 financial crisis have made it considerably less likely for the most common types of funds. That said, "rare" isn't "impossible," and every money market fund prospectus is legally required to disclose that your investment isn't guaranteed.
Pro Tip: Every money market fund prospectus includes some version of the sentence "you could lose money by investing in the fund." This isn't unusual boilerplate specific to one fund — the SEC's investor bulletin on money market funds confirms this disclosure is required across the industry precisely because these funds are investments, not deposits, however safe they're designed to be.
Money Market Fund vs. Money Market Account
This is the single most important distinction to understand, because the two products sound nearly identical and behave very differently:
| Factor | Money Market Fund | Money Market Account |
|---|---|---|
| What it is | A mutual fund that invests in short-term debt securities | A type of savings account offered by a bank or credit union |
| Regulated by | SEC | FDIC (banks) or NCUA (credit unions) |
| FDIC/NCUA insured? | No | Yes, up to $250,000 per depositor, per institution |
| Can the value decline? | Yes, in rare cases ("breaking the buck") | No — it's a deposit account, not an investment |
| Where you'd find it | Brokerage accounts (Fidelity, Schwab, Vanguard, etc.) | Banks and credit unions |
If your "money market" holding is inside a brokerage account and you bought it as an investment, it's almost certainly a money market fund. If it's a savings-style account at your bank, it's a money market account, deposit-insured the same way a regular savings account is. Confusing the two is exactly how people end up believing their brokerage money market fund carries a government guarantee it doesn't actually have.
How Money Market Funds Try to Hold a Stable $1.00
Government and retail money market funds use accounting methods that let them maintain a stable $1.00 share price under normal conditions, even though the actual market value of their underlying holdings fluctuates slightly day to day. As long as that underlying value stays within half a cent of $1.00, the fund keeps pricing shares at exactly $1.00 and passes earnings through as dividends instead of share-price appreciation.
This works well under normal market conditions because the fund only holds extremely short-term, high-quality debt — the kind of assets least likely to move much in price. The stability isn't a guarantee written into the fund by regulation; it's a byproduct of conservative, short-duration, high-credit-quality holdings that rarely move enough to break that half-cent threshold.
"Breaking the Buck": What It Means and When It's Happened
If a fund's actual underlying value falls more than half a cent below $1.00 per share, its board can (and generally must) reprice the fund below $1.00 — officially "breaking the buck." Investors holding shares at that moment would receive less than $1.00 per share when they redeemed.
This has happened only rarely in the decades money market funds have existed. The best-known case was the Reserve Primary Fund in September 2008, a large fund that held short-term debt issued by Lehman Brothers. When Lehman collapsed, the fund's value dropped enough to break the buck, triggering a wave of redemptions across the money market fund industry and prompting a temporary federal backstop program.
Since then, the SEC has repeatedly tightened the rules governing money market funds — including a 2016 reform that split institutional prime and tax-exempt funds into a "floating NAV" category, and a further 2023 reform (with compliance phased in through 2024) that added liquidity fees and removed "redemption gate" provisions for those same institutional fund types. Government and retail money market funds, which most individual investors use, were largely unaffected by these floating-NAV requirements and can still maintain the traditional stable $1.00 price.
Government vs. Prime vs. Municipal Money Market Funds
Not all money market funds carry the same risk, because they don't all hold the same investments:
- Government money market funds invest almost entirely in U.S. Treasury securities and other government-backed debt. This is the category most large brokerages (including Fidelity, Schwab, and Vanguard) use for their default "sweep" or settlement fund, and it carries the lowest risk of the three types.
- Prime money market funds invest in a broader mix that can include corporate commercial paper, making them somewhat more exposed to credit risk from the companies issuing that debt — this was the category the Reserve Primary Fund belonged to.
- Municipal (tax-exempt) money market funds invest in short-term municipal debt, offering income that's often exempt from federal (and sometimes state) tax, with risk tied to the creditworthiness of municipal issuers.
For most individual investors using a money market fund as a cash-equivalent holding inside a brokerage or retirement account, a government money market fund is the lowest-risk option among the three.
Are Money Market Funds FDIC Insured?
No. Money market mutual funds are investment products regulated by the SEC, not deposit products, and the FDIC explicitly excludes them from coverage regardless of which brokerage or fund company offers them. This holds true even for government money market funds that invest exclusively in Treasury securities — the fund itself still isn't FDIC insured, even though the underlying Treasuries carry the full faith and credit of the U.S. government.
This is different from a money market deposit account at a bank, which is FDIC insured up to $250,000 per depositor, per institution, the same as a regular savings account.
What SIPC Covers for Money Market Funds
If you hold a money market fund inside a brokerage account, SIPC coverage applies the same way it applies to any other security in that account: up to $500,000 in protection if the brokerage firm itself fails and can't return your holdings to you. SIPC does not protect against the fund's share price declining — that's ordinary investment risk, and it falls outside what SIPC exists to address, exactly as it does for stocks, bonds, or any other security.
The More Common Risk: Inflation, Not a Crash
For most people holding a money market fund, "breaking the buck" isn't the risk that actually affects them — inflation is. Money market funds are designed for capital preservation and modest income, not growth, so their returns tend to track short-term interest rates closely, minus whatever expense ratio the fund charges. When inflation runs higher than the fund's net yield, the purchasing power of that cash quietly erodes over time, even though the $1.00 share price never technically moves.
This is a normal trade-off, not a flaw: money market funds exist for short-term cash needs and stability, not long-term growth, so accepting a lower real return in exchange for low volatility is generally the point, not a surprise.
Common Misconceptions About Money Market Funds
- Assuming "money market" automatically means FDIC insured. Only bank money market deposit accounts carry FDIC insurance — money market mutual funds never do, regardless of what they invest in.
- Believing a stable $1.00 price is a legal guarantee. It's an accounting convention that works because of conservative holdings, not a regulatory promise that the fund can never lose value.
- Treating a government money market fund as identical to a savings account. It's still an investment product with a (very low, but nonzero) risk profile, not a deposit account.
- Confusing prime, government, and municipal funds as interchangeable. They carry meaningfully different risk profiles based on what they actually hold.
- Expecting money market fund returns to outpace inflation. These funds are built for stability and liquidity, not growth — treating idle cash sitting in one as a long-term investment ignores that trade-off.
FAQ: Money Market Fund Risk
Can a money market fund actually lose value? Yes, in rare cases known as "breaking the buck," if the fund's underlying investments decline enough that its share price falls below $1.00. This has happened only a handful of times in the industry's history.
Is a money market fund the same as a money market account? No. A money market fund is an SEC-regulated investment product; a money market account is an FDIC-insured deposit product offered by a bank or credit union. They are not interchangeable, despite the similar name.
Are money market funds FDIC insured? No, never — including government money market funds that invest in Treasury securities. FDIC insurance only applies to bank deposit products, not SEC-regulated investment funds.
What happened to the Reserve Primary Fund? It broke the buck in September 2008 after holding short-term debt issued by Lehman Brothers, which collapsed that same month. It remains the most well-known example of a money market fund failing to maintain its $1.00 share price.
Which type of money market fund is safest? Government money market funds, which invest almost entirely in U.S. Treasury and other government-backed securities, generally carry the lowest risk among the three main categories (government, prime, and municipal).
Does SIPC protect against a money market fund losing value? No. SIPC protects against brokerage firm failure, not against the fund's share price declining due to investment losses.
Is my money safer in a money market fund or a savings account? A savings account (or money market deposit account) is FDIC insured up to $250,000 and can't decline in value. A money market fund carries a small, non-zero risk of loss but has historically offered competitive yields with high liquidity. Which is more appropriate depends on your priorities and how much you value the FDIC guarantee versus the fund's yield and features.
Your Action Plan for This Week
Money market funds are about as low-risk as investment products get, but "very low risk" and "risk-free" aren't the same thing — and the name alone doesn't tell you which kind of protection actually applies.
- Check whether your "money market" holding is a fund (inside a brokerage account) or an account (at a bank) — the protections are genuinely different.
- If it's a fund, confirm whether it's a government, prime, or municipal fund, since the risk profile differs across the three.
- Don't assume FDIC insurance applies just because the fund invests in government securities — the fund itself is never FDIC insured.
- If you're holding a large cash balance for the long term, weigh whether a money market fund's stability is actually what you need, versus whether some of that money belongs in a longer-term diversified investment — like a 3-fund portfolio — instead.
