Finance

Rule of 72 Calculator

Estimate how long it takes to double money at a given annual growth rate using the Rule of 72 shortcut.

Last reviewed: April 30, 2026Free toolMethodology

Rule of 72 Calculator

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These fields start with sample inputs. Keep them or replace them, then run the tool to show a fresh result.

Number fields accept plain values and common formatted input such as 250000, 250,000, or 1,234.56.

Result

Calculating the sample result.

Why it matters

The Rule of 72 is a fast mental model for understanding the power of compounding without running a full future value calculation.

When to use

  • Sanity-checking growth assumptions
  • Explaining compounding in plain language
  • Comparing rough doubling times across return rates

Inputs & Outputs

Inputs

  • Annual rate is the expected yearly growth or inflation rate.

Outputs

  • Estimated doubling time shows the approximate number of years needed to double.
  • Exact doubling comparison gives a more precise log-based estimate alongside the shortcut.

Rule of 72 shortcut

Divide 72 by the annual rate expressed as a percentage. The result gives a quick estimate of the years required to double.

Doubling time ≈ 72 / annual rate

Worked example

1

Compounding shortcut

An asset grows at 8% annually.

Inputs

  • Annual rate: 8%

Steps

  • Doubling time ≈ 72 / 8 = 9 years

Result

  • At 8%, money roughly doubles every 9 years.

Edge cases & caveats

  • The shortcut is approximate, especially at very low or very high rates.
  • It is best used for quick intuition rather than formal projections.

Frequently Asked Questions

Why does the calculator also show an exact estimate?

Because the Rule of 72 is a shortcut. Showing the exact log-based doubling time helps users see how close the approximation is.

Can this apply to inflation too?

Yes. It can estimate how long it takes prices to double under a steady inflation rate.

Keep going

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