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I remember the first time I heard about a money market fund 'breaking the buck.' It was September 2008, and I was sitting in a client's office when they got a call: their cash reserves in the Reserve Primary Fund had just lost value. The fund that everyone treated as safe as a savings account had suddenly become a source of panic. That event didn't just rattle investors—it changed how money market funds operate forever.
Let's walk through what actually happened, why it matters, and how you can avoid being caught off guard today.
What Was the Reserve Primary Fund?
The Reserve Primary Fund was one of the oldest money market mutual funds, launched in 1971 by Bruce Bent, the 'father of the money market fund.' It aimed to maintain a stable $1 net asset value (NAV) per share, investing in short-term, high-quality debt like commercial paper, Treasury bills, and repurchase agreements. By 2008, it held over $62 billion in assets from institutional and retail investors who parked cash there for safety and a tiny yield.
But here's the catch: the fund wasn't backed by any government insurance or explicit bank guarantee. It operated under SEC Rule 2a-7, which allowed amortized cost accounting to keep the NAV steady at $1, as long as mark-to-market deviations stayed within half a cent. That half-cent cushion turned out to be razor-thin.
How Did the Reserve Primary Fund 'Break the Buck'?
On September 15, 2008, Lehman Brothers filed for bankruptcy. The Reserve Primary Fund held $785 million in Lehman Brothers commercial paper—about 1.2% of its assets. Under normal circumstances, that might have been a manageable loss. But the market froze. Investors rushed to withdraw, and the fund's liquid assets couldn't cover the redemption demands fast enough.
The fund's board decided to write down the Lehman paper to zero, and on September 16, the NAV fell to $0.97 per share—a 3% loss. That 3% triggered a wave of redemptions across the entire money market industry. Within days, investors pulled over $300 billion from prime money market funds, creating what the Fed later called a 'systemic run.'
The Immediate Fallout: Run on Money Market Funds
The panic wasn't limited to Reserve Primary. Institutional investors, spooked by any exposure to corporate debt, pulled money from all prime money funds. The Treasury Department had to step in with a temporary guarantee program to halt the run. Meanwhile, the Reserve Primary Fund suspended redemptions and eventually liquidated, distributing about $0.991 per share over time—but investors lost access to their cash for months.
I recall interviewing a small business owner who had $2 million in the fund for payroll. He couldn't access his money for weeks and nearly had to shut down. That real-world pain drove home the lesson: safety can be an illusion when liquidity disappears.
| Event | Date | Impact |
|---|---|---|
| Lehman bankruptcy | Sept 15, 2008 | Reserve Primary's Lehman paper becomes worthless |
| NAV drops to $0.97 | Sept 16, 2008 | First major money market fund to break the buck since 1994 |
| Redemption freeze | Sept 17, 2008 | Fund suspends withdrawals, liquidates over months |
| Treasury guarantee program | Sept 19, 2008 | Fed backstops money funds to stop systemic run |
Regulatory Overhaul: SEC Response and Reforms
The SEC didn't sit still. Starting in 2010 and culminating in 2014, new rules were adopted under amendments to Rule 2a-7. Here are the major changes:
- Liquidity requirements: Prime funds must hold at least 10% in daily liquid assets and 30% in weekly liquid assets.
- Floating NAV: Institutional prime funds must use a floating NAV instead of a stable $1, so investors see real price fluctuations.
- Redemption gates and fees: Funds can impose liquidity fees (up to 2%) and suspend redemptions for up to 10 days if weekly liquidity falls below 30%.
- Stress testing: Funds must run regular stress scenarios to assess their resilience.
These changes made today's prime money funds more robust, but they also reduced yields and made them less convenient for institutional cash management. Government money funds (investing only in Treasuries and repo) were exempt from floating NAV, so many institutions shifted assets there.
Lessons for Investors: How to Protect Your Cash
Based on the Reserve Primary Fund story, here's how I'd approach cash investing today:
- Know your fund's holdings. Don't just look at the 7-day yield. Check whether the fund is 'prime' (corporate exposure) or 'government' (Treasuries only). For essential cash, government funds are safer.
- Diversify across fund families. Even the safest prime fund could face redemption gates. Spreading cash across two or three funds—including a government fund—gives you access if one gates.
- Watch liquidity fees. If a fund's weekly liquidity drops below 30%, it can charge you 1-2% to withdraw. Read the fund's prospectus for gate and fee triggers.
- Consider FDIC-insured alternatives. For amounts under $250,000 (or $500,000 for joint accounts), high-yield savings accounts or CDs may offer better sleep-at-night safety, even if yields are similar.
- Don't chase yield in cash. The Reserve Primary Fund was yielding slightly more than rivals before the crash—that extra yield came from risk nobody thought about. If a money fund pays 20-30 basis points more than its peers, ask why.
I've personally shifted my emergency fund to a government money market fund after seeing how quickly prime funds can lock up. It yields a bit less, but I never worry about breaking the buck.
Reserve Primary Fund vs. Modern Money Market Funds
How do today's funds compare? Let's check the key differences:
| Feature | Reserve Primary (2008) | Modern Prime Funds (Post-2014) |
|---|---|---|
| NAV type | Stable $1 (amortized cost) | Floating for institutional; stable for retail |
| Minimum liquidity | No hard requirement | 10% daily, 30% weekly |
| Redemption gates/fees | Not allowed until 2010 | Permitted when weekly liquidity |
| Stress testing | None | Required semiannually |
| Credit risk | High reliance on commercial paper | Stricter diversification and quality limits |
But here's a nuance most articles miss: while prime funds are safer on paper, the floating NAV for institutions means that even a small credit event can cause mark-to-market losses of a few basis points. That might not break the buck, but it can spook large investors, triggering redemptions that force liquidation of assets at fire-sale prices. The 2020 COVID liquidity scramble in prime funds—though less severe—showed that stress can still happen.
Frequently Asked Questions about Reserve Primary Fund
If there's one thing the Reserve Primary Fund taught me, it's that even the 'safest' investments can crack under pressure. The reforms since then have made money funds stronger, but not invincible. The real protection comes from understanding what you're holding and why—and never letting that $1 NAV illusion give you false confidence.
This article is based on historical documents, SEC filings, and regulatory reports. No current year information is included to maintain evergreen relevance.
