Compound interest calculator
Enter a starting amount, an interest rate and a term and see at once what your money grows to, with interest on interest. If you add to it every month, fill that in too. Under the result you get a year-by-year table.
What you put in now. May be empty if you only save monthly.
The percentage per year, for example 3.5.
Part of a year is fine too, such as 2.5.
Optional. This amount is added at the end of every month.
Fill in the fields; the answer appears here straight away.
How it's worked out
How it works
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Enter the values
Type the numbers or the formula. Decimals may use a point or a comma. No idea? Click Fill in an example.
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Instant answer
The answer appears as you type, with the most important intermediate values.
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See the working
Under "How it's worked out" you see the steps, handy for checking your own calculation.
What is compound interest?
With compound interest you earn interest on your deposit and on the interest you earned before. That makes an amount grow faster and faster. Without deposits the formula is:
final amount = start × (1 + rate) ^ years
10,000 at 3.5% a year is, after 10 years, 10,000 × 1.035¹⁰ = 14,105.99. You have then received 4,105.99 in interest.
Adding every month
With 100 extra a month, paid in at the end of each month, the same example becomes 28,408.09: 22,000 paid in (10,000 + 120 × 100) and 6,408.09 in interest. The longer the term, the bigger the effect: 200 a month for 30 years at 4% gives 137,054.11, of which 72,000 is your own money.
Credited yearly, monthly or daily
If your bank credits interest more often, your money grows slightly faster. The tool turns this into the effective yearly return: 3.5% credited monthly is about 3.56% a year. You see that return under the result.
Good to know
Tax, fees and changing rates are not included, and returns on investments are not guaranteed. Use the result as an indication.
Frequently asked questions
Is the compound interest free?
Yes. The compound interest is completely free, with no account, sign-up or usage limit.
How accurate is the result?
The tool calculates with your browser's number precision. For important calculations, always double-check what you entered.
Does it work on my phone?
Yes. The tool works in any modern browser on a phone, tablet or computer.