Compound interest calculator
Enter the starting capital, contributions and rate to see how your money grows over time.
100% private — your files are processed on your device and never uploaded to a server.
How it works
- 1
Enter the starting capital
The amount you have to start investing today.
- 2
Add contributions and rate
If you'll contribute regularly, enter how much, then fill in the annual rate and how often interest compounds.
- 3
Check the result
You'll see the final total, how much you contributed, how much came from interest, and a year-by-year table.
How compound interest works
Unlike simple interest, with compound interest the interest earned each period gets added to the principal, and from then on it earns interest too. That's why growth accelerates over time — the longer the duration, the bigger the effect. This calculator assumes each recurring contribution lands at the end of each compounding period (it doesn't earn interest that same period), the most common convention for this kind of tool.
Compounding frequency matters: compounding monthly produces a slightly higher final result than compounding annually at the same nominal rate, because interest starts earning more interest more often.
Frequently asked questions
What's the difference between simple and compound interest?
With simple interest, interest is always calculated on the original principal. With compound interest, it's calculated on the principal plus interest already earned, so it grows faster over time.
When do my recurring contributions get added?
At the end of each compounding period (monthly, quarterly or annually, depending on what you pick). They don't earn interest in the same period they're added.
Which compounding frequency should I pick?
It depends on the real financial product you're simulating — check your bank's or investment's terms. At the same nominal rate, more frequent compounding gives a slightly higher final result.
Does this calculator account for inflation?
No. It calculates the nominal growth of your capital based on the rate you enter. To estimate real purchasing power, subtract expected inflation separately.