See how your money grows over time. Model initial investment, regular contributions, and compounding frequency.
| Year | Balance | Contributions This Year | Interest This Year | Total Invested |
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Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which only calculates on the principal), compounding means your money grows exponentially — you earn interest on your interest.
More frequent compounding means slightly faster growth. Daily compounding produces modestly more than monthly, which beats quarterly or annual. For long-term investments, the difference between daily and monthly compounding is usually small — what matters far more is the rate and time horizon.
The U.S. stock market (S&P 500) has returned roughly 10% annually before inflation and about 7% after inflation over long periods. Individual results vary significantly. This calculator uses whatever rate you input — we recommend modeling multiple scenarios to see a range of outcomes.
Time is the most powerful variable in compound interest. Someone who invests $5,000/year from age 25 to 35 (10 years) and stops will often end up with more at retirement than someone who starts at 35 and invests the same amount every year until retirement — because of the extra decades of compounding.