Compound Interest Calculator
Project how an investment or savings balance grows when interest compounds and you keep contributing every month.
| Year | Balance | Contributed | Interest |
|---|---|---|---|
| 2 | 16,087 | 14,800 | 1,287 |
| 4 | 22,812 | 19,600 | 3,212 |
| 6 | 30,243 | 24,400 | 5,843 |
| 8 | 38,454 | 29,200 | 9,254 |
| 10 | 47,527 | 34,000 | 13,527 |
| 12 | 57,551 | 38,800 | 18,751 |
| 14 | 68,628 | 43,600 | 25,028 |
| 16 | 80,867 | 48,400 | 32,467 |
| 18 | 94,390 | 53,200 | 41,190 |
| 20 | 109,333 | 58,000 | 51,333 |
How compound interest works
Compound interest means you earn interest not only on the money you put in, but also on the interest already earned. Each period, the interest is added to the balance, and the next period's interest is calculated on that larger balance. Over long horizons this produces exponential rather than linear growth.
This calculator compounds monthly: the annual rate is divided by 12 and applied to the balance each month, and your monthly contribution is added at the end of each month. The yearly table shows how the balance, your cumulative contributions, and the accumulated interest evolve.
Small differences matter enormously over time. One extra percentage point of annual return, or starting ten years earlier, can change the final balance by more than the total amount you contribute. That is why time in the market and fees are the two variables long-term savers watch most closely.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus all previously earned interest, so the balance grows faster over time.
How often does compounding happen in this calculator?
Monthly. The annual rate is divided by 12 and applied each month, which is a common convention for savings accounts and index-fund projections.
Is the projected result guaranteed?
No. The projection assumes a constant rate of return, which real investments do not deliver. Markets fluctuate, and actual results will differ — treat the output as an illustration, not a promise.
Does the calculation account for inflation or taxes?
No. Results are nominal, before taxes and inflation. To approximate real purchasing power, you can use an interest rate reduced by the expected inflation rate.