Compound Interest Calculator
Enter your starting principal, interest rate, and how often it compounds to see how your money grows over time. Add an optional recurring contribution to see how regular deposits accelerate your growth.
Results
| Future value | — |
|---|---|
| Total contributed | — |
| Total interest earned | — |
Year-by-year balance
| Year | Balance | Total contributed | Total interest |
|---|
How this calculator works
Compound interest means the interest you earn is added back to your balance, so future interest is calculated on a growing amount rather than just your original principal. The more frequently interest compounds — daily instead of annually, say — the sooner each bit of interest starts earning its own interest. At the same nominal annual rate, monthly compounding will always produce a slightly higher balance than annual compounding, because interest gets credited twelve times a year instead of once, and each credit compounds further before the year is out. The difference is small at low rates or short time horizons but grows noticeably over decades or at higher rates.
A recurring contribution compounds too: each deposit you add at the end of a period starts earning interest from that point forward, which is why starting early and contributing consistently matters more than the size of any single deposit.
A handy mental-math shortcut is the "rule of 72": divide 72 by your annual interest rate to estimate how many years it takes your money to double. At 7%, for example, 72 ÷ 7 ≈ 10.3 years — a quick sanity check without needing a calculator.
Results update automatically as you change any input above. This tool assumes a constant rate of return, which real investments rarely deliver year to year — actual results will vary.