Once you accept that cash should not sit in a 0.01% account, the next question is where it should sit instead. The two mainstream answers are a high-yield savings account (HYSA) and a money market fund (MMF), and they are frequently discussed as though they were interchangeable.
They are not. One is a bank deposit backed by government insurance; the other is an investment fund holding short-term instruments. This guide compares yield, protection, liquidity, and tax treatment, then gives a clear allocation framework by goal.
What Each One Actually Is
High-yield savings account
A deposit account at a bank or credit union, usually online-only, paying far more than a branch-based savings account because the provider carries lower overhead. Your money is a liability of the bank, protected by deposit insurance — up to $250,000 per depositor per institution in the US, and €100,000 per depositor per bank in the EU under the Deposit Guarantee Schemes Directive (£85,000 under the UK's FSCS).
Money market fund
A mutual fund holding very short-duration instruments: Treasury bills, government repurchase agreements, commercial paper, and certificates of deposit. It is a security, not a deposit. It is not covered by deposit insurance, though US funds fall under broker protection for custody failure (not for investment loss) and are tightly regulated on credit quality and maturity.
| Feature | High-yield savings | Money market fund |
|---|---|---|
| Legal form | Bank deposit | Investment fund |
| Typical yield | 3.50-5.00% APY | 4.00-5.20% (7-day yield) |
| Protection | Deposit insurance to statutory limit | No deposit insurance; diversified portfolio |
| Rate changes | Bank discretion, often lags policy cuts and hikes | Tracks short-term rates almost immediately |
| Access | 1-2 business days by transfer | 1-2 days to settle and withdraw |
| Minimum | Usually $0-$100 | Often $0-$3,000 depending on share class |
| Fees | None typically | Expense ratio 0.08-0.42%, netted from yield |
Yield, Safety, and the Trade-Off Between Them
Money market funds generally out-yield savings accounts by 0.2-0.7 percentage points because they pass through market rates directly rather than at a bank's discretion. Banks widen their margin when rates rise and are slow to pass increases on.
What the gap is worth
| Balance | At 4.20% (HYSA) | At 4.85% (MMF) | Annual difference |
|---|---|---|---|
| $10,000 | $420 | $485 | $65 |
| $25,000 | $1,050 | $1,213 | $163 |
| $100,000 | $4,200 | $4,850 | $650 |
| $250,000 | $10,500 | $12,125 | $1,625 |
Below roughly $25,000 the difference is real but small; above $100,000 it becomes a genuine decision — and that is also the point where deposit insurance limits start to matter.
How safe are money market funds?
Very, but not identically to a deposit. Government and Treasury-only funds hold sovereign-backed paper and are the most conservative category. Prime funds, which hold corporate commercial paper, carry a small credit component and can — in extreme stress — impose liquidity fees or gates under post-2016 rules. Two US funds have historically fallen below the $1.00 stable price, both during severe market dislocations.
Liquidity, Operations, and Tax Treatment
Speed of access, in practice
- HYSA: initiate a transfer and funds typically arrive in one to two business days; some providers offer instant transfers within the same banking group. Cards or ATM access are rare.
- MMF: sell the position and it settles same-day or next-day at most brokers, then a further day to reach an external bank. Money held at a broker you already use is effectively as fast.
Both are slower than checking, and neither should hold the cash you need for tomorrow's card payment. Keep two to four weeks of expenses in your current account regardless of which you choose.
Tax treatment
| Aspect | High-yield savings | Money market fund |
|---|---|---|
| US federal tax | Interest, taxed as ordinary income | Dividends, generally taxed as ordinary income |
| US state tax | Fully taxable | Treasury-only funds are often state-tax exempt in proportion to Treasury holdings |
| UK | Covered by the Personal Savings Allowance; cash ISA available | Taxable outside an ISA; can be held inside a stocks & shares ISA |
| EU | Varies; often withholding tax at source | Varies; may fall under investment fund taxation rules |
For a US resident in a high-tax state, a Treasury-only money market fund can beat a nominally higher HYSA rate after state tax. For a UK saver with a modest balance, a cash ISA or the Personal Savings Allowance may make the savings account effectively tax-free.
Choosing Per Goal: A Practical Allocation
The right answer is usually both, split by purpose.
| Money | Best home | Why |
|---|---|---|
| 2-4 weeks of spending | Current / checking account | Instant access outweighs yield |
| Emergency fund, first 3 months | High-yield savings | Insured, simple, no market mechanics |
| Emergency fund, months 4-6 | Government MMF or T-bill fund | Higher yield, access still within days |
| House deposit within 3 years | Either; ladder term deposits for known dates | Capital certainty is mandatory on a fixed date |
| Cash above the insurance limit | Government MMF or Treasuries | Diversified sovereign exposure beats uninsured deposits |
| Business operating reserve | MMF at the brokerage | Same-day settlement and no per-institution limit issue |
A three-point checklist before you move money
- Compare like with like: APY against 7-day yield, both net of fees.
- Check the introductory-rate trap: many advertised savings rates drop after three to twelve months, or apply only to balances below a cap.
- Confirm transfer limits and timing before the fund becomes your emergency reserve — some accounts cap withdrawals per month.
Whichever you choose, run the target through the savings goal calculator with the account's real rate so the monthly contribution reflects the interest the account will genuinely contribute.