See how a starting amount plus steady monthly contributions can grow over the years — and how much of the final balance is interest doing the work for you.
Compound interest is the reason patient saving beats almost everything else over long stretches. Each period you earn a return not just on your original money, but on the interest it has already earned. Those earnings join the balance and go on to earn more — so a line that starts nearly flat curves upward and eventually climbs steeply.
This calculator compounds monthly. Every month it adds your contribution and applies one twelfth of your annual return to the whole balance. Two forces stack up: your starting amount growing on its own, and a growing stream of monthly deposits, each of which has its own runway to compound.
What is compound interest?
Interest earned on both your original money and the interest it has already earned. Because each period's earnings join the balance, growth accelerates over time.
How much difference do the extra years make?
A lot. The final years add the most because the balance is largest then. Doubling your horizon usually more than doubles the ending balance.
Is the return guaranteed?
No. This tool applies a fixed annual return you choose. Real returns vary year to year and can be negative — treat the result as a planning estimate, not a promise.