Compound Interest Calculator
Work out the future value of savings or an investment with compound interest, monthly contributions and your choice of compounding frequency.
Inputs
Future value
Future value
How compound interest grows your money
With compound interest, you earn interest on your interest. Each period, the gain is added to the balance, and the next period's interest is calculated on that larger amount. Year to year the change feels small, but over a couple of decades the curve bends sharply upward. At 7% a year, money roughly doubles about every 10 years. The lesson is simple: start early and stay consistent.
How to use the calculator
Enter your starting amount, how much you plan to add each month, the expected annual rate, how many years you will invest and how often interest compounds. The calculator adds each monthly contribution at the end of the month and shows the final balance, how much of it you put in, and how much came from interest. The yearly table shows the balance growing over time, and you can download it as a CSV.
What moves the result most
- Time. Extra years matter more than almost anything else, because growth builds on growth.
- Rate. A difference of one or two points adds up to a large gap over long periods.
- Consistency. Regular monthly contributions do a lot of the heavy lifting.
- Compounding frequency. More frequent compounding helps a little, but much less than time or rate.
Frequently asked questions
Is 7% a realistic rate?
Over long periods, broad US stock market returns have averaged roughly 10% a year before inflation, or about 7% after inflation. Returns vary a lot from year to year and are not guaranteed, so 7% is a common, fairly conservative planning assumption.
Does this include taxes, fees or inflation?
No. Results are before taxes and fees. To see the value in today's dollars, enter a rate that is already adjusted for inflation.
What is the difference between the nominal and effective rate?
The nominal rate is the stated annual rate. The effective rate includes compounding within the year, so monthly compounding at 7% works out to slightly more than 7% over a full year.