Interest on interest is why a small habit grows into a large sum. This compound interest calculator shows what a starting amount and regular deposits become after a number of years at a given rate. It reports the final balance, how much you paid in, how much the interest added and how long it takes for the money to double, plus a table with the balance at the end of every year.
Calculate growth in four steps
- Enter the starting amount and the monthly deposit. Either can be zero.
- Type the expected interest rate per year and the number of years.
- Choose how often interest is added: annually, quarterly, monthly or daily.
- Read the final balance, the split between deposits and interest, and the table by year.
What the numbers mean
- Final balance is everything you hold at the end.
- Total deposits are the starting amount plus every monthly deposit.
- Interest earned is the difference, the part the rate produced on its own.
- Time to double is how long a lump sum needs at this rate and compounding, without further deposits.
Why frequency and time matter
The same 5% gives 1.628895 times the money after ten years with yearly compounding and 1.647009 times with monthly compounding. The frequency is a small effect compared with time and with the deposit. Starting ten years earlier usually beats paying in more later, because the early money has more years to earn interest on interest. Try 20 years against 30 years at the same deposit to see the gap.
Limits of the estimate
Real returns are not constant: shares rise and fall, savings rates change. The calculator uses one fixed rate, ignores taxes, fees and inflation, and assumes deposits at the end of each month. Treat the result as a scenario, not a forecast, and lower the rate to see a cautious case.
Nothing is sent anywhere
The arithmetic runs in your browser. Your savings figures are not uploaded or stored.