Rule of 72 Doubling Time Calculator
The Rule of 72 approximates the number of years T required to double an investment at a fixed annual compound rate r via T = K / r (where K = 72 for annual compounding).
Years required for capital to double (2.0x)
Annualized rate of return in percent
72 for standard annual rates (69.3 for continuous compounding)
Step-by-Step Calculation
The Rule of 72 approximates the number of years T required to double an investment at a fixed annual compound rate r via T = K / r (where K = 72 for annual compounding).
Real-World Reference Values
Balanced 60/40 portfolio doubling cadence
Global equity historical doubling pace
Exact mathematical limit as compounding frequency → ∞
20-Row Comparison Table
Doubling Time (T) · Annual Compound Rate (r (%))
| # | Annual Compound Rate (r (%)) | Doubling Time (yr) | Δ % |
|---|---|---|---|
| 01 | 0.5 | 144 yr | +1500.00% |
| 02 | 1.4122 | 50.9853 yr | +466.50% |
| 03 | 2.3243 | 30.9765 yr | +244.18% |
| 04 | 3.2365 | 22.2462 yr | +147.18% |
| 05 | 4.1487 | 17.3549 yr | +92.83% |
| 06 | 5.0609 | 14.2268 yr | +58.08% |
| 07 | 5.973 | 12.0542 yr | +33.94% |
| 08 | 6.8852 | 10.4572 yr | +16.19% |
| 09 | 8 Current | 9 yr | 0.00% |
| 10 | 8.7095 | 8.2668 yr | -8.15% |
| 11 | 9.6217 | 7.4831 yr | -16.85% |
| 12 | 10.5339 | 6.8351 yr | -24.05% |
| 13 | 11.4461 | 6.2904 yr | -30.11% |
| 14 | 12.3582 | 5.8261 yr | -35.27% |
| 15 | 13.2704 | 5.4256 yr | -39.72% |
| 16 | 14.1826 | 5.0767 yr | -43.59% |
| 17 | 15.0947 | 4.7699 yr | -47.00% |
| 18 | 16.0069 | 4.4981 yr | -50.02% |
| 19 | 16.9191 | 4.2556 yr | -52.72% |
| 20 | 17.8313 | 4.0379 yr | -55.13% |
Frequently Asked Questions
Why does the Rule of 72 use 72 instead of 69.3?+
While ln(2) × 100 = 69.3147 is exact for continuous compounding, discrete annual compounding around 6%–10% is closer to 72, which is also cleanly divisible by 2, 3, 4, 6, 8, 9, and 12.
How do I find the return rate needed to double my money in 6 years?+
Click SOLVE FOR on r (%) and set T = 6. With K = 72, the required compound annual growth rate is 12%.
Can the Rule of 72 measure purchasing power halving from inflation?+
Yes. At 4% annual inflation, cash purchasing power halves in 72 / 4 = 18 years.