How to calculate compound interest
- Enter your starting amount and how much you will add every month. Either can be 0.
- Enter the yearly interest rate, the number of years, and how often interest is compounded.
- Read the final balance, how much you put in, and how much came from interest. The chart and table show every year.
- Tick "today's money" and set an inflation rate to see the result in today's buying power.
Try changing only one number at a time. Adding years or a higher rate usually matters far more than a change in how often interest is compounded.
Questions
Are my numbers stored or sent anywhere?
No. Everything is calculated in your browser. Nothing is uploaded, saved, or tracked.
What is compound interest?
It is interest earned on your starting amount and also on the interest already added. A balance of 10,000 at 7% a year becomes about 10,700 after one year, and the next year the 7% is applied to 10,700, not to 10,000. Over many years this snowball effect becomes large.
How does the compounding frequency change the result?
More frequent compounding adds interest to the balance more often, so it earns slightly more. For 7% a year, yearly compounding gives 7.00% and daily compounding gives about 7.25% over a year. The difference is small compared with the effect of the rate and the number of years.
What does the inflation-adjusted view show?
Prices usually rise over time, so a future amount buys less than the same number does today. Turning on "today's money" divides each balance by the cumulative inflation, so you can see what the growth is worth in today's buying power. The inflation rate is your own assumption.
When is the monthly amount added?
At the end of each month, after that month's interest. Interest is worked out from the yearly rate and your chosen compounding frequency. This is a simplified model for learning and planning, not a promise of future returns or financial advice.
Credits
Built by OneTooling using standard browser features. No third-party code runs on your data.