Rule of 72 Table: Years to Double by Interest Rate (2026)
The Rule of 72 gives a fast estimate of how long it takes money to double: divide 72 by the annual rate. Below is the complete table for rates from 1% to 25%, alongside the exact doubling time so you can see the difference.
Quick answer: To estimate years to double, use Years ≈ 72 ÷ Rate%. At 6% that is about 12 years; at 8% about 9 years. The exact doubling time is ln(2) ÷ ln(1 + Rate%).
Rule of 72 Calculator
Rule of 72 estimate
12.0 years
72 ÷ 6%
Exact doubling time
11.90 years
ln(2) ÷ ln(1 + 6%)
Complete Rule of 72 Table (1%–25%)
| Annual Rate | Rule of 72 (72 ÷ Rate) | Exact Double Time | Difference |
|---|---|---|---|
| 1% | 72.0 yrs | 69.66 yrs | +2.34 yrs |
| 2% | 36.0 yrs | 35.00 yrs | +1.00 yrs |
| 3% | 24.0 yrs | 23.45 yrs | +0.55 yrs |
| 4% | 18.0 yrs | 17.67 yrs | +0.33 yrs |
| 5% | 14.4 yrs | 14.21 yrs | +0.19 yrs |
| 6% | 12.0 yrs | 11.90 yrs | +0.10 yrs |
| 7% | 10.3 yrs | 10.24 yrs | +0.04 yrs |
| 8% | 9.0 yrs | 9.01 yrs | -0.01 yrs |
| 9% | 8.0 yrs | 8.04 yrs | -0.04 yrs |
| 10% | 7.2 yrs | 7.27 yrs | -0.07 yrs |
| 11% | 6.5 yrs | 6.64 yrs | -0.10 yrs |
| 12% | 6.0 yrs | 6.12 yrs | -0.12 yrs |
| 13% | 5.5 yrs | 5.67 yrs | -0.13 yrs |
| 14% | 5.1 yrs | 5.29 yrs | -0.15 yrs |
| 15% | 4.8 yrs | 4.96 yrs | -0.16 yrs |
| 16% | 4.5 yrs | 4.67 yrs | -0.17 yrs |
| 17% | 4.2 yrs | 4.41 yrs | -0.18 yrs |
| 18% | 4.0 yrs | 4.19 yrs | -0.19 yrs |
| 19% | 3.8 yrs | 3.98 yrs | -0.20 yrs |
| 20% | 3.6 yrs | 3.80 yrs | -0.20 yrs |
| 21% | 3.4 yrs | 3.64 yrs | -0.21 yrs |
| 22% | 3.3 yrs | 3.49 yrs | -0.21 yrs |
| 23% | 3.1 yrs | 3.35 yrs | -0.22 yrs |
| 24% | 3.0 yrs | 3.22 yrs | -0.22 yrs |
| 25% | 2.9 yrs | 3.11 yrs | -0.23 yrs |
Exact doubling time uses the closed-form compounding formula ln(2) ÷ ln(1 + r). Positive “Difference” means the Rule of 72 slightly overestimates the time to double at that rate.
How the Rule of 72 Works
Compound interest grows a balance by a fixed percentage each period. The time to double solves (1 + r)n = 2, which gives the exact answer n = ln(2) ÷ ln(1 + r). The number 72 is a convenient stand-in: it is divisible by many small integers (2, 3, 4, 6, 8, 9, 12…), making mental math easy, and it tracks the true value closely for typical savings and investment returns.
You can reuse the same shortcut in reverse — to find the rate needed to double in a target number of years, divide 72 by the years. It also works for decay: at 3% inflation, purchasing power halves in about 24 years (72 ÷ 3).
Sources & Methodology
- Doubling-time formula and the Rule of 72: standard compound-interest mathematics (closed-form solution of (1 + r)n = 2). Source: foundational finance/algebra reference; retrieval August 2026.
- Exact values computed in-page with JavaScript:
ln(2) ÷ ln(1 + rate/100). No external or “current” market rate is assumed, so the table does not go stale. - For a worked narrative and examples, see the Rule of 72 calculator and the complete Rule of 72 guide.
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Daniel Okafor · Lead Financial Editor, CFP®
Reviewed by Priya Nair, CFP®, Independent Content Reviewer.