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Compound Interest Calculator

See how an investment grows when interest compounds — and how regular monthly contributions accelerate it. Adjust the rate, time and contributions to watch the difference.

Your plan

Future value
$143,000
  • Starting amount
  • Contributions
  • Interest earned
Total contributed
Total interest
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How it works

Compound growth of a starting balance, plus regular contributions, is:

FV = P(1 + r/n)nt + PMT × [ ((1 + r/n)nt − 1) / (r/n) ]

Worked example

$10,000 start + $200/mo for 20 years at 7%, compounded monthly:

Frequently asked questions

What does compounding frequency change?
More frequent compounding (daily vs annually) slightly increases the total because interest starts earning interest sooner. The effect is real but modest compared to the rate and time horizon.
Why does time matter so much?
Compound growth is exponential, so the last few years add far more than the first. Starting earlier — even with smaller amounts — usually beats starting later with larger ones.
Is this calculator before or after inflation?
It shows nominal growth. To estimate buying power, subtract your expected inflation rate (e.g. use 4% instead of 7%) for a rough 'real' return.

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