Balance at the end
0.00
Enter a time period greater than zero. Amounts and the interest rate cannot be negative, and you need a starting amount or a monthly contribution.
Total you put in
Interest earned
0.00Estimates only. Contributions are added at the end of each month. Real returns vary, and taxes and fees are not included.
How this compound interest calculator works
Enter the amount you start with, how much you add each month, the yearly interest rate and how many years you will save. The calculator shows what your balance could grow to, how much of it is your own money and how much is interest.
What is compound interest?
Compound interest means you earn interest on your interest. Each time interest is added, it becomes part of the balance, and the next interest payment is calculated on the larger amount. Over many years this snowball effect becomes much bigger than simple interest, which only ever pays on the original amount.
The formula behind it
For a lump sum, the future value is the starting amount times (1 + rate divided by the number of compounding periods per year), raised to the power of the number of periods. Regular monthly contributions are added the same way, one payment at a time. This calculator converts your chosen compounding frequency into an equivalent monthly rate, so all four options work with monthly contributions.
Example
Start with 10,000, add 500 every month and earn 5% a year, compounded monthly, for 20 years. You put in 130,000 of your own money (10,000 plus 240 payments of 500). The balance grows to about 232,643, so roughly 102,643 is interest. In another example, 10,000 at 5% with no extra deposits grows to about 16,470 after 10 years with monthly compounding, and to about 16,289 with annual compounding.
How to grow your savings faster
- Start early. Time matters more than almost anything else, because each year of growth builds on the last.
- Add money regularly. Even small monthly amounts add up. Try changing the contribution above.
- Leave it alone. Withdrawals interrupt the snowball effect.
- Compare rates. A higher rate has a large effect over long periods.
Frequently asked questions
Does compounding frequency matter?
A little. More frequent compounding gives slightly more growth, but the interest rate and the time you save for matter much more.
What is the difference between simple and compound interest?
Simple interest is paid only on the original amount. Compound interest is paid on the original amount plus all interest already earned, so it grows faster.
Can I use this for loans?
Loans also use compound interest, but they need a payment formula. For that, use our loan payment calculator.