About This Compound Interest Calculator
This free online compound interest calculator helps you estimate how an investment can grow over time. By combining your starting amount, annual rate, time period, and optional monthly contributions, you can quickly understand the future value of your savings or investment plan.
Compound interest is powerful because your investment earns returns, and then those returns begin earning returns too. Over longer periods, this can significantly increase total growth compared with simple interest.
Compound Interest Formula
Future Value = P × (1 + r / n)^(n × t) + PMT × [((1 + r / n)^(n × t) - 1) / (r / n)]
- P = initial principal
- r = annual interest rate (decimal)
- n = number of times interest compounds per year
- t = number of years
- PMT = recurring contribution per compounding period
Why Compound Interest Matters
- Growth on growth: Interest is calculated on both principal and previously earned interest.
- Time advantage: The earlier you start, the more time your money has to compound.
- Regular deposits help: Small monthly contributions can make a major difference over time.
- Useful for planning: Great for retirement, education savings, emergency funds, and long-term goals.