Compound interest calculator
Compounding means earning a return on returns already earned. Add a monthly contribution and the effect grows sharply with time — which this shows year by year.
USD
USD
%
years
%
Value at the end$111,787
- Total you contribute
- $64,000
- Gains
- $47,787
- Estimated tax on gains
- $7,168
- Value after tax
- $104,619
- Growth multiple
- 1.75
Local rule · United StatesInterest is taxed as ordinary income; long-term capital gains at 0%, 15% or 20% depending on income.
The formula
FV = P(1 + i)^n + PMT · ((1 + i)^n − 1) / i, with i the periodic rate and n the number of periods. Contributions are made at the end of each period.
Worked example
10,000 at 6% for 15 years with 300 a month compounded monthly grows to 111,528. You put in 64,000, so 47,528 is growth.
How to use it
- 1Use a realistic long-run return. Historic equity averages are nominal, before inflation.
- 2Pick the compounding frequency your account actually uses.
- 3The tax rate defaults to your country's rule; change it if your account is tax-sheltered.
Questions people ask
Should I use a nominal or a real return?
Either, as long as you are consistent. Enter a nominal return to see future money, or subtract inflation first to see the result in today's purchasing power.
Does compounding frequency matter much?
Less than people expect. At 6%, moving from yearly to monthly compounding adds about 0.17 percentage points of effective annual return.
Last reviewed: 2026-10-20