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Compound Interest Calculator

See what savings grow to with compound interest and regular contributions. Splits the result into what you paid in and what the interest added.

Balance after 20 years

$170,619.05

Interest earned

$100,619.05

143.7% on top of what you paid in

You paid in

$70,000.00

$10,000.00 plus contributions

Contributed monthly

$250.00

Nominal figures. To think in today’s money, subtract expected inflation from the rate before entering it.

How to use the Compound Interest Calculator

  1. Enter your starting balance. The amount you already have set aside.
  2. Add rate and time. Use the annual rate and how many years it will compound for.
  3. Add contributions. Include a regular monthly amount to see how much it changes.

Frequently asked questions

What does compounding frequency actually change?
It sets how often earned interest starts earning interest itself. More frequent compounding at the same nominal rate produces slightly more, with the gain flattening out quickly beyond monthly.
Why do the later years grow so much faster?
Because interest is earned on the whole balance, including previously earned interest. Growth is exponential rather than linear, so most of the total tends to arrive in the final third of the period.
Is inflation accounted for?
No. Results are in nominal terms. To think in today’s money, subtract the expected inflation rate from the growth rate before entering it, which gives an approximate real return.
Are contributions added before or after interest?
At the end of each period, which is the conservative convention. Contributing at the start of each period instead would produce a slightly higher figure than the one shown.

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