Calculateur de marche monetaire

Money Market Calculator

Money market accounts occupy a useful middle ground between a standard savings account and a short-term CD — they pay competitive interest while keeping your money accessible. This calculator shows how your balance grows over any time frame given your starting deposit, monthly additions, and the account’s APY. The results let you compare projected earnings between institutions, estimate how long it takes to hit a savings target, and understand how much a difference in APY actually costs you in real dollars.

How Money Market Interest Is Calculated

Most money market accounts compound interest daily and credit it to your balance monthly. The daily accrual formula is:

Daily Interest = Current Balance x (APY / 365)

For projections that include ongoing monthly contributions, the standard future value formula applies:

FV = PV x (1 + r)^n + PMT x [(1 + r)^n - 1] / r

Where PV is the opening balance, PMT is the monthly deposit, r is the monthly rate (APY / 12), and n is the number of months. Because money market APYs are variable and can be changed by the bank at any time, actual results will differ from projections if the rate shifts during the period.

Worked Examples

Example 1 — Emergency fund, no additions. You park a $15,000 emergency fund in a money market account at 4.50% APY and make no further deposits. After 12 months you earn $680 in interest, bringing the balance to $15,680. After 3 years the balance reaches $17,131 — a $2,131 gain with zero effort beyond the initial deposit.

Example 2 — Building a down payment. You open a money market account with $5,000 and add $500 per month at 4.75% APY. After 24 months you have deposited $17,000 total. Interest earned = $936, giving you a $17,936 balance — enough, with a little more time, for a 3.5% FHA down payment on a $450,000 home.

Example 3 — High-balance account. You move $80,000 in idle cash into a money market account at 5.00% APY with no monthly additions. After 1 year you earn $4,081 (daily compounding vs. $4,000 simple interest — the $81 difference represents the daily compounding benefit). After 5 years the balance reaches $102,102, earning $22,102 in interest.

Money Market Growth Reference Table

When to Use This Calculator

• You want to know exactly how much more a 4.75% APY account earns versus a 3.00% account over 2 years on a specific balance
• You are building an emergency fund and want to know when your balance will reach 3 or 6 months of expenses
• You are comparing a money market account against a short-term CD for a specific savings goal with a known timeline
• You received a large windfall — an inheritance, bonus, or home sale proceeds — and want to see projected earnings before deciding where to place it
• You are evaluating whether a higher-balance tier (which unlocks a better APY) is worth maintaining given your typical balance

Common Mistakes

1. Comparing APR to APY across institutions. Some banks advertise the nominal rate (APR) while others show the effective yield (APY). These numbers look similar but APY is always higher because it includes compounding. Always convert to APY before comparing — use the APY calculator to convert any stated APR.

2. Ignoring fees. A $10 monthly maintenance fee on a $2,000 balance at 4.50% APY costs you $120/year in fees but earns only $90 in interest — a net loss of $30. Always factor monthly fees into your net yield calculation. Many online banks charge no monthly fees at all.

3. Treating the promotional rate as permanent. Many banks offer introductory rates of 5.00%+ that drop to 3.00% or lower after 3—6 months. If you project growth at the promotional rate for 2 years, your estimate could be off by hundreds of dollars. Read the terms carefully and model a rate drop after the intro period ends.

4. Confusing a money market account with a money market mutual fund. Bank money market accounts are FDIC-insured up to $250,000. Money market mutual funds offered through brokerages are not — they are SEC-regulated investment products that, while generally stable, can theoretically lose value. The two products have the same name but different risk profiles.

Current Context for 2026

The Federal Reserve held rates in the 4.25%—4.50% range through early 2026, keeping money market account yields elevated by historical standards. The best online money market accounts are paying 4.50%—5.00% APY — compare that to the 0.01%—0.10% paid by most traditional bank savings accounts. This spread means the difference between using a major national bank and an online bank for a $50,000 emergency fund is roughly $2,200—$2,500 per year in lost interest. That rate gap is unlikely to persist indefinitely — when the Fed eventually cuts rates further, money market yields will drop within weeks. Locking in competitive rates now, or at least moving cash to a high-yield account, is straightforward and FDIC-insured.

Tips

1. Shop money market rates at least quarterly — rates shift frequently and the bank that led the market 6 months ago may now be mid-pack
2. Keep your emergency fund (3—6 months of expenses) in a money market account rather than a checking account — the same liquidity, meaningfully more interest
3. If your balance regularly stays above $25,000—$50,000, ask your bank about tiered or relationship rate tiers that may increase your APY
4. Set up automatic monthly transfers from checking to your money market account — consistent contributions turn a parking account into a growth engine
5. Check whether your money market account offers check-writing — useful for large, infrequent expenses like property tax or insurance premiums without the friction of transfers
6. At tax time, money market interest is reported on Form 1099-INT and taxed as ordinary income; if you are in a high bracket, compare after-tax yield against tax-exempt alternatives

Related Calculations

• APY Calculator — convert any stated APR to APY so you can compare accounts on equal footing
• Compound Interest Calculator — model long-term growth with variable compounding frequencies
• CD Calculator — compare money market flexibility against a CD’s locked-in rate for a fixed term