Compound Interest Calculator
Estimate how money grows with compound interest. Choose your compounding frequency, add regular contributions, and see a full year-by-year breakdown.
Your investment
Added every period at the frequency selected above.
An assumption you choose, not a guaranteed rate. Try different values to see how they affect the projection.
Estimated future value (monthly compounding)
$300,851
Based on a 7.00% assumed annual rate over 20 years, compounded monthly. This is a projection, not a guarantee.
Total contributions
$130,000
Interest earned
$170,851
Estimated total return
131.42%
Year-by-year breakdown
| Year | Starting balance | Contributions | Investment growth | Ending balance |
|---|---|---|---|---|
| 1 | $0 | $16,000 | $919 | $16,919 |
| 2 | $16,919 | $6,000 | $1,419 | $24,339 |
| 3 | $24,339 | $6,000 | $1,956 | $32,294 |
| 4 | $32,294 | $6,000 | $2,531 | $40,825 |
| 5 | $40,825 | $6,000 | $3,148 | $49,973 |
| 10 | $93,671 | $6,000 | $6,968 | $106,639 |
| 15 | $168,587 | $6,000 | $12,383 | $186,971 |
| 20 | $274,790 | $6,000 | $20,061 | $300,851 |
How compound interest is calculated here
This calculator uses the standard compound-interest formula, extended to include regular contributions at the frequency you choose. Your initial amount compounds at the assumed rate, and each contribution is added on schedule and given the remaining time in the plan to grow. For the exact formulas and rounding rules, see our methodology page.
Want to see the mechanism explained in plain English first, with a small worked example? Read how compound interest works.
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Frequently asked questions
This is an educational calculator, not financial advice.
Results shown are estimated future values based on the return assumption you enter — they are not predictions and VOO is not guaranteed to achieve any particular return. Past performance of the S&P 500 or any fund does not guarantee future results. Consider speaking with a licensed financial professional before making investment decisions.