Alternative doubling-time shortcut
Rule of 70 Calculator
The Rule of 70 is a simple shortcut for estimating how long it takes money, earnings or even prices to double. It is similar to the Rule of 72, but many people prefer it for lower growth assumptions or when thinking about inflation and economic growth.
How it works
Years to double ≈ 70 ÷ annual growth rate (%)
At 5%, the Rule of 70 gives about 14 years. At 2% inflation, it gives about 35 years for prices to double.
When it is useful
- Lower growth or inflation-style estimates
- Quick mental math in personal finance
- Comparing different growth assumptions side by side
Rule of 70 vs Rule of 72
| Shortcut | Best use | Main idea |
|---|---|---|
| Rule of 70 | Lower growth rates, inflation, simple intuition | Slightly cleaner for slower growth assumptions. |
| Rule of 72 | Common investing returns | Widely used for rates like 6%, 7% and 8%. |