๐ Compound Interest Calculator
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Enter your starting principal, annual return, time horizon, compounding frequency, and optional monthly contributions to project the future value of an investment or savings account. Includes a year-by-year balance breakdown.
Estimate only โ not financial advice. Real returns vary and are not guaranteed.
How to use
- Enter your starting principal โ the amount you have today.
- Enter the expected annual return as a percent (historical S&P 500 average is ~7% real, ~10% nominal).
- Enter the time horizon in years.
- Pick the compounding frequency: yearly, monthly, or daily. Most index funds compound continuously โ monthly is a close approximation.
- Optionally add a monthly contribution. Click Calculate.
Formula: FV = P(1 + r/m)mยทt + C ยท ((1 + r/m)mยทt โ 1) / (r/m), where P is principal, r is the annual rate, m is compounding periods per year, t is years, and C is the periodic contribution converted to the compounding period.
Inflation, taxes, and fees are not modeled. A 7% nominal return at 3% inflation is roughly a 4% real return โ the future balance will buy less than today's purchasing power suggests.