Compound interest calculator
Compound interest, with contributions.
See how a starting amount grows when interest compounds, and what regular contributions add over time.
Calculator
Assumptions. Interest compounds at the frequency you choose. Contributions are treated as an equivalent amount per compounding period (contribution × contribution frequency ÷ compounding frequency), which matches the usual closed-form formula when the two frequencies are the same. At a 0% rate, the future value is simply the starting amount plus all contributions. Returns aren’t guaranteed.
How compound interest grows
Compound interest means each period’s interest is added to the balance, so later periods earn interest on a larger amount. More frequent compounding grows a balance slightly faster at the same nominal annual rate. Regular contributions add new principal that then compounds too.
Formula
Worked example
Starting with $10,000 at 7% a year, compounded monthly for 10 years, grows to about $20,096.61 with no contributions. Adding $100 every month raises the future value to about $37,405.09, of which $12,000 is contributions and the rest is growth.
When to use it
- Rough savings or investment growth estimates at an assumed rate of return.
- Comparing monthly versus yearly compounding, or the effect of regular deposits.
- Not tax, fee or inflation adjusted, and not investment advice. For a loan payment instead, use the loan calculator or mortgage calculator.