Money Market Account Calculator

How it is calculated

The balance is computed with the standard compound-interest formula FV = P × (1 + r ÷ n)n × t, where P is the deposit, r is the rate you enter as a decimal (4.5 becomes 0.045), n is the number of compounding periods per year and t is the term in years. Interest is FV − P. Dollar amounts are shown with two decimals, and the term may be fractional.

Important detail: the tool takes the percentage in the rate field as a yearly rate that is then divided by n and compounded, which is how a nominal rate works. A real APY already includes compounding, so entering an advertised APY here with monthly compounding counts the compounding twice and slightly overstates the result. To project a stated APY exactly, set compounds per year to 1. The deposit, term and compounding count must be above zero, the rate zero or more, and no deposits or withdrawals are modelled during the term.

Common mistakes

• Entering an advertised APY and also choosing monthly or daily compounding. The tool compounds the entered rate again, so the result is a little too high; use compounds per year = 1 to follow an APY exactly.
• Typing the rate as a decimal (0.045) instead of a percentage (4.5). A rate of 0.045 means 0.045% and shows almost no interest.
• Entering the term in months. The field is in years, so 18 months is 1.5, not 18.
• Assuming monthly deposits are included. Only the starting deposit grows; regular contributions need a different calculator.
• Treating the rate as fixed for the whole term. Money market rates are variable, so the result is a projection at today's rate, not a promise, and it ignores fees, minimum balances and taxes.