Compound Interest Calculator
See exactly how your money grows with compound interest. Future value, monthly contributions, Rule of 72, and investment timeline.
📖 About Compound Interest Calculator
Compound interest earns interest on both your original principal and previously earned interest — creating exponential growth. This is why starting to invest early is so powerful: a 25-year-old investing $200/month at 8% will have over $700,000 by age 65, while a 35-year-old doing the same will have only $300,000.
📜 History
Compound interest has been used for over 4,000 years. Mathematician Jacob Bernoulli discovered the constant e (≈2.71828) in 1683 while studying continuously compounded interest. The Rule of 72 dates to at least 1494, appearing in Luca Pacioli's Summa de arithmetica.
🎯 Common Uses
- Retirement savings planning
- Investment portfolio analysis
- Savings goal projection
- Loan cost comparison
- Education fund planning
- Wealth building strategy
FAQ's
❓ What is compound interest formula?
A = P(1 + r/n)^(nt) where A=final amount, P=principal, r=annual rate, n=compounds per year, t=years. Add regular contributions for realistic projections.
❓ How does compounding frequency affect growth?
Daily compounding grows slightly faster than monthly, which grows faster than annual. The difference is small for low rates but compounds over decades.
❓ What is the Rule of 72?
Divide 72 by the annual return rate to estimate doubling time. At 8% annual return, money doubles in 72÷8=9 years.
❓ How much should I invest monthly?
Even $100/month at 8% for 30 years grows to $150,000. $500/month becomes $745,000. The key is consistency and starting early.