A money market account (MMA) sits somewhere between a savings account and a checking account: it usually pays a higher interest rate than a normal savings account, comes with limited check-writing or debit-card access, and is FDIC-insured up to the legal limit. The catch is that the rate banks advertise is an annual percentage yield, and what your balance actually grows to depends on how long you leave it untouched and how often interest compounds.
This money market calculator takes your starting deposit, the advertised MMA APY, and the number of months you plan to save, then projects your ending balance and the interest you earned. It also runs the same math against a regular savings account so you can see, in dollars, exactly how much extra the higher MMA rate is worth over your chosen term.
How to Use
- Enter your Initial Deposit — the amount you are putting into the money market account today. This is the principal that interest builds on.
- Set the Money Market APY. Your bank's rate sheet or account page shows this as an annual percentage yield; a competitive MMA often pays 4.0%–5.0% while a traditional savings account pays far less.
- Choose the Term (Months). Twelve months is the default, but you can model a 6-month emergency-fund hold, a 24-month savings goal, or any other horizon.
- Optionally adjust the Regular Savings APY comparison figure. The default is 1.0%, close to what many brick-and-mortar savings accounts still pay, but raise or lower it to match the alternative account you actually have.
- Read the result card: your money market ending balance and interest earned sit next to the regular-savings projection, with the MMA advantage called out separately.
The engine compounds interest monthly, which is the convention most banks use for high-yield money market accounts. Interest credited each month then earns interest itself the following month, so the growth is slightly larger than simply multiplying the rate by the principal.
The Money Market Growth Formula
The calculator uses the standard compound interest future-value formula:
FV = P × (1 + r/12)ⁿ
Where:
- FV is the ending balance after the term.
- P is the initial deposit (principal).
- r is the annual rate as a decimal — the advertised APY divided by 100.
- n is the number of months money stays in the account.
The monthly rate is the annual rate divided by 12, and interest is applied at the end of each month. Interest earned is simply the ending balance minus the principal you started with.
Worked example on a $25,000 deposit at 4.50% APY for 12 months: the monthly rate is 0.045 ÷ 12 = 0.00375, and the balance grows to $26,148.50. That is $1,148.50 of interest — noticeably more than the $1,000 you would get from simple (non-compounding) interest, because each month's interest immediately starts earning on the next month's balance. If the rate is 0%, the formula reduces to the principal itself, and the ending balance equals the starting deposit with no interest at all.
How an MMA Differs From a Savings Account
Money market accounts and high-yield savings accounts are both insured cash vehicles, but they are not identical products:
- Rate. MMAs and high-yield savings accounts both pay market-driven variable rates, and the gap between them is usually small today. The old advantage of MMAs paying more has narrowed, but promotional MMA rates can still beat a stagnant local savings account.
- Access. Federal rules limit convenient withdrawals and outgoing transfers from savings and money market accounts to a small number per statement cycle. MMAs often add a debit card or paper checks, which makes them more flexible than a plain savings account but less liquid than a checking account.
- Minimums. Some MMAs require a higher opening deposit or minimum balance to earn the advertised APY, and may charge a fee if you dip below it.
- Safety. Both are FDIC-insured at banks or NCUA-insured at credit unions up to the coverage limit, so principal is protected the same way either way.
The reason to run the comparison in this calculator is that a 3.5-percentage-point rate gap sounds small, but on a six-figure balance over several years it is thousands of dollars.
Examples
Example 1 — The default $25,000 at 4.50% for a year. Deposit $25,000 into an MMA at 4.50% APY, compounded monthly for 12 months. The ending balance is $26,148.50, and interest earned is $1,148.50. The same $25,000 in a regular savings account at 1.0% grows to $25,251.15, earning only $251.15. The MMA advantage over the year is about $897.35 — free money from switching accounts.
Example 2 — A large emergency fund. Keeping $1,000,000 in cash at 4.50% APY for 12 months compounds to $1,045,939.83, earning $45,939.83. At a 1.0% savings rate the same money earns only $10,045.96. The rate gap is worth roughly $35,893.86 in a single year — which is why parking large cash reserves in the highest insured yield matters so much.
Example 3 — A short-term goal. If you deposit $10,000 at 4.50% for just 6 months, monthly compounding grows it to about $10,227.84, or roughly $227.84 of interest. Slide the Term control down to 6 to see how a shorter horizon still captures the rate advantage, just over fewer compounding periods.
FAQ
How is money market interest calculated?
The calculator uses the compound interest future-value formula FV = P × (1 + annualRate/12)ⁿ, where P is your initial deposit, annualRate is the advertised APY divided by 100, and n is the number of months. Interest earned equals the ending balance minus the principal. This is the same monthly-compounding convention banks use for high-yield money market accounts.
Is a money market account better than a savings account?
A money market account can pay a comparable or slightly higher rate and often adds limited check or debit access, while still being FDIC-insured. Whether it is better depends on the actual APY, minimum balance, and withdrawal limits. Use the Regular Savings APY field in this calculator to compare your specific alternatives in dollars.
What is the difference between APY and interest rate?
The interest rate is the nominal annual rate before compounding, while APY (annual percentage yield) is the effective rate after compounding over a year. This calculator takes the advertised APY and compounds it monthly, which is the standard way banks present money market yields.
Are money market accounts safe?
Yes. Money market accounts at banks are FDIC-insured, and at credit unions they are NCUA-insured, up to the legal coverage limit. That means your principal is protected even if the institution fails, unlike an uninsured investment. Always confirm the account is at an insured institution.
How much can I withdraw from a money market account?
Federal rules historically limited convenient withdrawals and outgoing transfers from savings and money market accounts to a small number per monthly statement, though enforcement has been relaxed. Banks still set their own limits and may charge fees or convert the account if you exceed them. Treat an MMA as a savings vehicle, not an everyday checking account.
Do money market rates change over time?
Yes. Most money market accounts pay variable rates that rise and fall with the broader interest-rate environment. The calculator assumes a constant APY for the whole term; in reality, your actual balance will track whatever rate your bank sets each month, so re-check the rate periodically.
Disclaimer
This money market calculator is provided for informational purposes only and does not constitute financial, banking, or investment advice. Projections are based on the constant-rate monthly-compounding formula and the inputs you enter; actual money market account yields are variable, may require minimum balances, and can change at any time. Regular-savings comparison figures are illustrative. Always confirm current rates, fees, minimums, and insurance coverage directly with your bank or credit union before choosing where to hold your cash.