Compound interest means you earn returns on your past returns, not just on what you put in. This compound interest calculator projects how an initial investment and regular contributions could grow over time, with your choice of compounding frequency. It also converts the result into today’s dollars so you can see the effect of inflation.
Compound Interest Calculator
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The compound interest formula
For a single deposit, future value = P × (1 + r/n)n × t, where P is the principal, r the annual rate, n the number of compounding periods per year and t the number of years. The calculator adds each contribution month by month so you see the full picture.
What drives growth
- Time: starting 10 years earlier can matter more than contributing more later.
- Rate of return: small differences compound into big gaps over decades.
- Consistency: automatic monthly contributions keep you on track. See dollar-cost averaging.
- Costs and taxes: fees and taxes reduce your effective return, so tax-advantaged accounts help.
Investment returns are not guaranteed, and values can fall. Use conservative assumptions when planning.
Related: Retirement & 401(k) Calculator, How the Stock Market Works, Investment Strategies for Beginners, All Financial Calculators.