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Investing $500 a month
| Annual return | 10 years | 20 years | 30 years |
|---|---|---|---|
| 4% | $73,625 | $183,387 | $347,025 |
| 6% | $81,940 | $231,020 | $502,258 |
| 8% | $91,473 | $294,510 | $745,180 |
| 10% | $102,422 | $379,684 | $1,130,244 |
Monthly compounding, contributions at the end of each month, before taxes and fees. You'd contribute $60,000, $120,000 and $180,000.
Assumptions
- Contributions are made at the end of each month. Returns are steady every year (real investments go up and down). Before taxes and fees.
Frequently asked questions
What is compound interest?+
Interest earned on both your original money and the interest it has already earned. Over long periods, growth on growth becomes the biggest part of the balance.
What's the compound interest formula?+
For a lump sum: A = P × (1 + r/n)^(n×t), where P is the principal, r the annual rate, n compounding periods per year and t years. Regular contributions add the future value of each deposit; the calculator does this month by month.
What is the rule of 72?+
Divide 72 by the annual return to estimate how many years it takes money to double: about 10 years at 7.2%, 12 years at 6%, 18 years at 4%.
Does compounding frequency matter much?+
A little. At 5%, monthly compounding gives an effective 5.12% a year and daily about 5.13%, versus 5.00% yearly. The rate and time matter far more.
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Last reviewed October 15, 2026. Calculator version 1.0.0. Results are estimates for educational purposes, not financial, tax or lending advice. How we check our numbers.