A money market account works like a savings account with a higher interest rate and optional check-writing access. Here is a precise breakdown of the mechanics — how your money earns interest, how the bank uses your deposits, and what you can and cannot do with the account.
How Interest Is Calculated and Credited
Money market accounts pay interest based on your daily balance:
- Daily accrual: The bank calculates interest each day using the formula: Daily Interest = (Balance x APY) / 365
- Daily compounding: Most MMAs compound daily — meaning earned interest is added to your balance and itself earns interest the next day
- Monthly crediting: The accumulated daily interest is deposited into your account once per month
Worked example: You have a $15,000 balance in an MMA earning 4.20% APY.
- Daily interest: ($15,000 x 0.042) / 365 = $1.726 per day
- Monthly interest (30 days): approximately $51.78
- Annual interest: approximately $630
What the Bank Does With Your Money
When you deposit into a money market account, the bank pools your funds with other deposits and invests them in short-term, low-risk instruments:
| Investment type | What it is |
|---|---|
| U.S. Treasury bills | Short-term government debt (4-week to 52-week) |
| Agency securities | Debt from government-sponsored entities (FHLB, FNMA) |
| Repurchase agreements | Short-term collateralized loans to other institutions |
| CDs from other banks | Short-term certificates of deposit |
This is why the rate is called a “money market” rate — banks are literally investing in the money markets. They earn a return, pay you a portion as APY, and keep the spread.
Accessing Your Money
| Method | Availability | Speed |
|---|---|---|
| Check writing | Many MMAs (not all) | 1–5 business days to clear |
| Debit card | Some MMAs | Instant at point of sale |
| ACH transfer to linked bank | All MMAs | 1–3 business days |
| Wire transfer | Most MMAs (may have fee) | Same day |
| ATM withdrawal | Rare — usually requires debit card | Instant |
| In-branch withdrawal | Traditional banks only | Instant |
Withdrawal Rules in 2026
Federal Reserve Regulation D previously capped savings and MMA withdrawals at 6 per month. That cap was permanently removed in April 2020. You can now make as many withdrawals as allowed by your bank’s own terms.
However, individual banks may impose:
- Their own per-month transaction limits
- Fees ($5–$15) for withdrawals above a threshold
- Minimum balance requirements that trigger fees if your balance drops too low
Always check your specific account’s terms.
How the Rate Changes Over Time
Money market account rates are variable — they adjust when the Federal Reserve changes the federal funds rate:
| Fed action | Typical MMA response | Timing |
|---|---|---|
| Fed raises rates | MMA rates increase | Within 1–4 weeks |
| Fed cuts rates | MMA rates decrease | Within 1–4 weeks |
| Fed holds rates | MMA rates stable | Until next change |
This means your APY is not guaranteed to stay the same. If you want a locked-in rate, a CD is the alternative — but you give up flexibility.
Money Market Account Mechanics Summary
| Feature | How it works |
|---|---|
| Interest | Accrues daily; credited monthly |
| Compounding | Daily (standard) |
| Rate type | Variable (moves with Fed rate) |
| Access | Transfer, check (if offered), debit (if offered) |
| Withdrawal limit | Per bank terms (federal cap removed in 2020) |
| Insurance | FDIC / NCUA up to $250,000 |
For a complete overview of what a money market account is, see what is a money market account. For the safety of these accounts, see are money market accounts safe and are they FDIC insured. For the full pros and cons, see money market account pros and cons.
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