Use the Rule of 72 to see how long it takes to double money at any interest rate. Interactive 2026 calculator.
| Time Period | 5% Return | 7% Return | 10% Return |
|---|---|---|---|
| 5 years | $32,084 | $35,441 | $41,133 |
| 10 years | $41,175 | $50,242 | $67,676 |
| 20 years | $67,816 | $100,968 | $183,202 |
| 30 years | $111,694 | $202,912 | $495,935 |
The fastest way to estimate how long it takes to double your money is the Rule of 72: divide 72 by your annual interest rate. At 7%, money doubles in approximately 10.3 years. At 10%, it doubles in 7.2 years.
This rule works remarkably well for rates between 2% and 20%. The exact formula is: years = ln(2) ÷ ln(1 + rate). At 7%, that's ln(2)/ln(1.07) = 10.24 years. The Rule of 72 estimate of 10.3 years is very close.
Understanding doubling time helps contextualize investment decisions. At 7% (approximate S&P 500 real return), a $10,000 investment becomes $20,000 in ~10 years, $40,000 in ~20 years, and $80,000 in ~30 years — without adding a single dollar.
Divide 72 by your annual interest rate to get the approximate years to double your money. At 8%: 9 years. At 6%: 12 years. At 12%: 6 years. It's accurate within 1% for rates between 2–20%.
At 7% annual return, money doubles in approximately 10.3 years (exact) or 10.3 years by Rule of 72. This is roughly the historical real return of the S&P 500.
To double in exactly 10 years, you need a 7.18% annual return (ln(2)/10 × 100%). Rule of 72: 72 ÷ 10 = 7.2% — very close.