Should I Use a HYSA or Money Market for Cash?

Quick answer

This question is really three questions because "money market" means three different things:

• HYSA: bank deposit, FDIC-insured, principal protected to $250K/depositor/bank/category.
• Money Market Deposit Account (MMDA): also a bank deposit, also FDIC-insured. Functionally similar to HYSA. Some allow limited check-writing.
• Money Market Mutual Fund (MMF): investment product at a brokerage. SIPC-protected (different mechanism), can technically break the buck (rare), often higher yield.

The HYSA vs. MMDA question is mostly cosmetic. The HYSA vs. MMF question matters.

Why this matters

The difference in mechanism is the difference in worst case. If a bank fails, FDIC makes you whole the next business day. If a money market mutual fund "breaks the buck" (NAV drops below $1.00), you can lose a small percentage of principal, Reserve Primary Fund in 2008 fell to ~$0.97, costing holders ~3%.

For most people, the practical risk of a MMF breaking the buck is near-zero in normal markets. But if your reason for holding cash is "I want zero risk to principal," HYSA is the stricter answer.

Worked example with $ numbers

On $100K, the yield spread between top HYSA and top MMF is typically $0-$200/year. Not life-changing, but real.

Tax angle (often overlooked)

Treasury money market funds (like Vanguard VUSXX) hold 99%+ Treasury bills. Treasury interest is exempt from state income tax. For CA, NY, NJ, MA residents in high brackets, this can swing the after-tax math toward Treasury MMFs even when the headline yield is identical to a HYSA.

Example: $250K at 4.25% = $10,625 interest. At CA's 9.3% state bracket, HYSA loses ~$988 to state tax. A Treasury MMF at the same 4.25% loses $0 to state tax, a $988/year after-tax edge from the state-tax exemption alone.

When the answer changes

• You want true zero risk to principal. HYSA. Full stop.
• You want same-day access tied to a brokerage where you trade. MMF.
• You're in a high-state-tax state and care about after-tax. Treasury MMF (VUSXX, SGOV ETF as alternative).
• Your cash is over the FDIC cap and you want to avoid splitting across banks. MMF inside a brokerage often gets you above $250K without the multi-bank shuffle.
• You're at a bank with weak digital infrastructure. A brokerage MMF often has cleaner ACH, faster wires, better statements.

Common mistakes

• Confusing MMDA (bank, FDIC) with MMF (mutual fund, SIPC). They sound the same, they're different products with different safety mechanisms.
• Buying a prime MMF in a high-stress market. Prime MMFs (hold commercial paper) carry more credit risk than government or Treasury MMFs. The 2008 break-the-buck was a prime fund. Government MMFs have a stronger record.
• Holding cash in a low-yield default brokerage sweep. Many brokerages default to a 0.50% bank sweep instead of a money market fund (7-day yields of 3.45-3.76% at SPAXX and VUSXX on September 23, 2026). Check what your idle cash is actually earning.
• Ignoring expense ratios. MMFs charge fees (often 0.10-0.30%) baked into the quoted yield. The 7-day SEC yield is post-fee.

When a CD or MYGA enters the picture

HYSAs and MMFs both float with the Fed. Neither protects you from a cutting cycle. For cash you won't need for 1+ years, the structural answer is a fixed-rate vehicle, CD, T-bill at known maturity, or MYGA, not a marginally-higher-yielding floating product.

Use the HYSA-vs-MMF debate to optimize the part of your cash that needs to stay liquid. Use CDs and MYGAs to lock the part that doesn't.

What to do next

• If you have a brokerage account already and your cash is sitting in the default sweep, check the sweep yield. If it's under 1%, manually move it to the brokerage's MMF (e.g., SPAXX, VMFXX, SNVXX).
• If you're a CA/NY/NJ/MA resident with $50K+ of cash, run the math on a Treasury MMF (VUSXX) vs. your HYSA after state tax.
• For cash you won't need for 1+ years, get fixed-rate CD and MYGA quotes.
• If the horizon is closer to three years than three months, the floating-vs-locked question is the real one: HYSA or MYGA for 3-year money.

Follow-up Questions

Disclosure

This article is general educational information, not personalized financial, tax, or legal advice. HYSA APYs, CD rates, and MYGA rates change frequently, confirm current figures with the bank or carrier and the actual contract or account agreement before acting. FDIC insurance covers deposits at member banks up to $250,000 per depositor, per insured bank, per ownership category. State insurance guaranty associations cover annuity contracts up to state-specific limits (typically $250,000-$300,000). Hans Goldstein is an independent licensed insurance producer (NPN 20602398). No compensation has been received from any bank or carrier in connection with this article. Past rates do not predict future rates. Tax discussion reflects federal law as of 2026 and is subject to change; consult a CPA for your specific situation.