A quick mental shortcut: 72 ÷ interest rate ≈ years to double. Then verify using the calculator.
Test doubling in Money GrowthThe Rule of 72 estimates doubling time:
Years to double ≈ 72 ÷ (annual return %)
Example: at 6% return → 72 ÷ 6 ≈ 12 years to double.
It’s an approximation. Real markets fluctuate, and contributions/fees/tax change outcomes. Still useful for intuition.
72 has many divisors, so it works well as a shortcut across common return rates.
It’s usually close for moderate rates. For very low or very high rates, it becomes less precise.
No. It’s about doubling a lump sum. Use the calculator to include ongoing contributions.
No. Inflation affects purchasing power, not the nominal doubling time.
Use /grow.html with a lump sum and set years near the estimate to check the result.