Compound Interest Calculator

See how your money grows when interest earns interest. Enter a starting amount, a monthly deposit, a rate and a time period.

When to use this calculator

Use this calculator to see the effect of time on money. Compound interest means you earn interest on your interest, so the longer you leave money invested, the faster it grows. It works for savings accounts, investment projections and long-term goals.

Example future balances

How this calculator works

Interest is added to your balance at the compounding interval you choose, and the next interest payment is calculated on the larger balance. We convert your rate into an equivalent monthly rate, then grow the starting balance and add each monthly deposit at the end of the month. Deposits are assumed to be made once a month.

Step-by-step example

Using these inputs: Starting balance ($): 5000; Monthly deposit ($): 200; Annual interest rate (%): 6; Years to grow: 20; Compounding: Monthly.

Starting with $5,000 and adding $200 a month at 6% for 20 years gives $108,959. You put in $53,000, so $55,959 comes from interest, a growth multiple of 2.06x.

Tips for a better estimate

• Start early. Time matters more than the size of the deposits.
• Check how often interest compounds. Monthly compounding grows slightly faster than yearly.
• Use a conservative rate for planning. Higher advertised returns are not guaranteed.

FAQ

What is compound interest?

It is interest calculated on both your original money and the interest already earned. Over many years this makes growth speed up.

Does more frequent compounding matter?

It helps a little. Daily compounding earns slightly more than yearly at the same rate, but the rate and the time matter far more.

Are taxes included?

No. Interest in a taxable account may be taxed. Retirement accounts can change this.

What is the Rule of 72?

Divide 72 by the yearly rate to get a rough number of years to double your money. At 6%, it takes about 12 years.

What is the difference between APR and APY?

APY includes the effect of compounding, so it is the better number to compare savings accounts.

Does this include taxes or inflation?

No. Taxes and inflation reduce what your money is really worth, so use the inflation calculator for the buying-power view.

Rates and limits last updated: October 2026. This is an estimate for general information only, not financial, tax or legal advice.

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