Rule of 72 Calculator
Interest Rate%
Initial Amount$
Doubling Time (Rule of 72)
10.3 years
Exact Doubling Time
10.2 years
Tripling Time
16.2 years
10x Time
34 years
Reference Table
| Rate | Rule of 72 | Exact | Difference |
|---|---|---|---|
| 1% | 72 yrs | 69.7 yrs | +2.3 yrs |
| 2% | 36 yrs | 35 yrs | +1 yrs |
| 3% | 24 yrs | 23.4 yrs | +0.6 yrs |
| 4% | 18 yrs | 17.7 yrs | +0.3 yrs |
| 5% | 14.4 yrs | 14.2 yrs | +0.2 yrs |
| 6% | 12 yrs | 11.9 yrs | +0.1 yrs |
| 7% | 10.3 yrs | 10.2 yrs | 0 yrs |
| 8% | 9 yrs | 9 yrs | 0 yrs |
| 9% | 8 yrs | 8 yrs | 0 yrs |
| 10% | 7.2 yrs | 7.3 yrs | -0.1 yrs |
| 11% | 6.5 yrs | 6.6 yrs | -0.1 yrs |
| 12% | 6 yrs | 6.1 yrs | -0.1 yrs |
| 13% | 5.5 yrs | 5.7 yrs | -0.1 yrs |
| 14% | 5.1 yrs | 5.3 yrs | -0.1 yrs |
| 15% | 4.8 yrs | 5 yrs | -0.2 yrs |
Doubling Illustration
| Doubling | Value | Year |
|---|---|---|
| Start | $10,000 | 0 |
| 1x | $20,000 | 10.2 |
| 2x | $40,000 | 20.5 |
| 3x | $80,000 | 30.7 |
| 4x | $160,000 | 41 |
| 5x | $320,000 | 51.2 |
| 6x | $640,000 | 61.5 |
| 7x | $1,280,000 | 71.7 |
| 8x | $2,560,000 | 82 |
| 9x | $5,120,000 | 92.2 |
| 10x | $10,240,000 | 102.4 |
Methodology
Rule of 72: years ≈ 72 / rate
Exact: years = ln(2) / ln(1 + r/100)
Rate = 7%Initial = $10,000
The Rule of 72 is a quick mental math shortcut for estimating doubling time. It works best for rates between 2-15%. For tripling time, use ln(3)/ln(1+r). For 10x time, use ln(10)/ln(1+r).