Calculate monthly compound interest with optional recurring deposits. See your balance grow month by month.
| Time Period | 5% Return | 7% Return | 10% Return |
|---|---|---|---|
| 5 years | $53,253 | $57,061 | $63,398 |
| 10 years | $102,346 | $116,687 | $143,028 |
| 20 years | $246,206 | $321,044 | $489,606 |
| 30 years | $483,145 | $731,733 | $1,427,805 |
Monthly compounding means interest is calculated and added to your balance 12 times per year. This is the most common compounding frequency for investment accounts, 401(k) plans, and mutual funds.
The formula: A = P × (1 + r/12)^(12×t) + PMT × [(1 + r/12)^(12×t) - 1] / (r/12), where PMT is the monthly contribution. At 7% for 15 years with $15,000 initial and $500/month, the final balance exceeds $240,000.
Monthly contributions are particularly powerful because each deposit immediately begins earning returns. The earlier in the month you contribute (or set up automatic transfers), the more each dollar compounds over time.
A = P(1 + r/12)^(12t) + PMT × [(1 + r/12)^(12t) - 1] / (r/12), where P is principal, r is annual rate, t is years, and PMT is monthly contribution.
$500/month at 7% for 20 years grows to approximately $261,000 from roughly $120,000 in total contributions — more than double your invested money through compounding.
Research shows lump sum investing outperforms dollar-cost averaging in rising markets roughly 67% of the time. However, for most people, consistent monthly investing is more practical and builds the habit of saving.