Compound Interest Calculator
See how money grows when interest earns interest. Enter a starting amount, an annual interest rate, how long you plan to save, how often interest compounds and an optional monthly deposit. Amounts work in any currency.
- Future balance
- 54,713.58
- Total deposits
- 34,000.00
- Interest earned
- 20,713.58
How it’s calculated
A single deposit P at an annual rate r, compounded n times a year for t years, grows to:
A = P × (1 + r/n)n·t
With continuous compounding the formula becomes A = P × er·t.
Monthly deposits D are added at the end of each month. Each one grows at the equivalent monthly rate i = (1 + r/n)n/12 − 1, so all deposits together are worth:
FV = D × ((1 + i)12·t − 1) / i
The future balance is A + FV. Interest earned is the balance minus everything you deposited.
Examples
One deposit, compounded annually
You put 5,000 in an account paying 5% a year, compounded annually, and leave it for 10 years. A = 5,000 × 1.0510 = 8,144.47, so you earn 3,144.47 in interest.
Small start, steady monthly deposits
You start with 1,000 and add 100 every month for 20 years at 6% compounded monthly. You deposit 25,000 in total, and the balance reaches 49,514.29: 24,514.29 of it is interest.
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on both your original deposit and the interest already added to it. Because each period starts from a larger balance, growth speeds up over time, unlike simple interest, which is only ever paid on the original amount.
Does compounding frequency make a big difference?
More frequent compounding gives a slightly higher result, but the gap is small at ordinary rates. 1,000 at 5% for 10 years becomes 1,628.89 with annual compounding and 1,648.72 with continuous compounding, the maximum possible.
What is the difference between APR and APY?
APR is the stated yearly rate before compounding. APY (annual percentage yield) already includes the effect of compounding over one year. If your bank quotes an APY, enter it with annual compounding to get the same result.
How long does it take to double my money?
A quick estimate is the rule of 72: divide 72 by the annual rate. At 6% money doubles in about 12 years. For an exact answer, enter your rate here and adjust the years until the balance is twice the deposit.
Are taxes, fees or inflation included?
No. The result is the nominal balance before taxes, account fees and inflation. To estimate growth in today’s money, subtract the expected inflation rate from the interest rate as a rough adjustment.
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Results are estimates for general information and are not financial, medical or legal advice.