Compound Interest Calculator
See exactly how your money grows over time — principal, contributions, and compounding, all together.
Investment details
Balance over time
How compounding builds wealth over time
Compound interest means you earn returns not just on what you put in, but on the returns you've already earned — the effect accelerates the longer money stays invested. Enter a starting amount, an optional monthly contribution, an expected annual return, and a time horizon to see the year-by-year breakdown between what you contributed and what compounding added on top.
Also useful: Budget Calculator and Real Estate Deal Calculator.
Frequently asked questions
There's no guaranteed rate — many long-term planning estimates use 6-8% for a diversified stock portfolio, but actual returns vary year to year and aren't guaranteed. Try a few rates to see a range of outcomes.
It matters less than people expect — monthly versus annual compounding on the same rate typically changes the final result by a small amount compared to the effect of the rate itself or the time horizon.
Each year's interest is calculated on a larger balance than the year before, so the dollar amount of interest earned compounds and accelerates the longer the money stays invested — this is most visible in the later years of a long time horizon.