Compound interest calculator
Enter what you start with, what you add each month, the yearly return and the number of years.
What you enter stays on this page and is not sent anywhere.
- Total after 20 years
- $300,851
- You put in
- $130,000
- Interest earned
- $170,851
At 7% a year, money doubles in about 10.2 years.
Growth over time
You put in Interest earned
How to use it
- Type the starting amount and how much you add each month. Either can be 0.
- Enter the yearly rate and the number of years, and pick monthly or yearly compounding.
- Add a tax rate on the gain or tick today's money to take inflation out of the result.
Questions
What formula does this compound interest calculator use?
The starting amount grows as P x (1 + r/k)^(k x t), with k = 12 for monthly or 1 for yearly compounding. Contributions go in at the end of each period: every month with monthly compounding, or twelve months' worth once a year with yearly compounding.
How long does it take to double my money?
At a fixed yearly rate r, money doubles after ln 2 / ln(1 + r) years. At 7% that is about 10.2 years. The calculator shows this figure for the rate you enter.
Why tick the option for today's money?
Prices rise over time, so a large sum in 20 years buys less than the same sum today. With an inflation rate entered, every amount is divided by (1 + inflation)^years so you can compare it with prices now.
Is the return guaranteed?
Only for fixed-rate savings. Stock and fund returns change from year to year, so a steady rate is a planning figure. Fees also lower the real return.
More tools
