See how your money grows over time with compound interest and optional monthly contributions — with a year-by-year table and chart.
| Year | Contributed | Interest Earned | Balance |
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Compound interest is interest calculated on both your original principal and the interest you've already earned. Unlike simple interest, which only ever grows on the starting amount, compound interest snowballs — each period's interest gets added to the balance, and then earns interest itself in the next period. Over long time periods, this compounding effect is what turns modest, regular saving into significant growth.
The standard formula is A = P(1 + r/n)nt, where A is the final amount, P is the starting principal, r is the annual interest rate (as a decimal), n is how many times per year interest compounds, and t is the number of years.
More frequent compounding means interest starts earning its own interest sooner, which produces slightly more growth at the same stated rate. Monthly compounding out-grows annual compounding, and daily compounding out-grows monthly — though the practical difference is usually small unless the interest rate is high or the time period is very long.
Adding a fixed monthly contribution meaningfully increases the final balance, because every contribution starts compounding from the moment it's added rather than sitting idle. Over long horizons — 15, 20, 30 years — consistent monthly contributions often account for more of the final balance than the interest earned on the original principal alone, which is why "starting early" matters so much for long-term saving.
Compound interest is interest calculated on both the original principal and the interest already earned in previous periods. Unlike simple interest, which only grows on the original amount, compound interest causes a balance to grow faster over time because each period's interest is added to the balance that earns the next period's interest.
The compound interest formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is how many times per year interest compounds, and t is the number of years. For example, $10,000 at 7% compounded annually for 10 years grows to about $19,671.51.
More frequent compounding produces slightly more growth, because interest starts earning its own interest sooner. Monthly compounding grows a balance faster than annual compounding at the same rate, though the difference is usually small unless the rate is high or the time period is very long.
Adding a fixed monthly contribution significantly increases the final balance, because each new contribution also starts compounding from the moment it's added. Over long time periods, consistent monthly contributions often account for more of the final balance's growth than the original principal alone.