What Is Compound Interest?
Compound interest is the process where the interest earned on an investment is reinvested, generating additional interest over time. It's the engine behind exponential growth in finance.
Unlike simple interest (where only the initial principal earns interest), compounding means your principal grows each period — you earn interest on your interest.
Albert Einstein reportedly called it "the eighth wonder of the world" — and for good reason: a $1,000 investment at 10% annual returns grows to over $17,000 in 30 years, with no additional contributions.
The Compound Interest Formula
A = P (1 + r/n)nt
- A = Total amount (principal + interest)
- P = Initial principal
- r = Annual interest rate (decimal)
- n = Compounding periods per year
- t = Time in years
Why Compounding Matters
The single most important factor in compounding is time. The earlier you start investing, the more your money can grow. Our calculator lets you visualize this effect with your own numbers.
Experiment with different scenarios: adjust compounding frequency, change periodic contributions, account for inflation, or see how taxes impact your returns.
Common Use Cases
- 📈 Retirement planning — See how much to save each month
- 🏦 Savings accounts — Compare interest rates and terms
- 📚 Financial education — Teach the power of compounding
- 💼 Investment funds — Project your portfolio growth
- 🎓 College savings — Plan education funds for your family