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Finance

Rule of 72 Calculator

Approximate the years needed to double a balance at a constant positive annual rate.

Amounts stay on this deviceMethod and assumptions below
Financial workspace
Financial workspace

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Use the Calculate button to see your result.

Estimate based on your inputs and the stated assumptions.

How to use this tool

  1. Enter annual growth rate.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

Input reference and sample values

Use the units and choices shown for each field. Sample values are provided for practice, not as recommendations.

InputFormat and unitsSample
Annual growth rateNumeric value. Unit: %. Must be greater than zero. Maximum: 100.8

Result for these sample inputs

9 years
Exact annual-compounding doubling time
9.00646834

Rule-of-72 approximation, not a guaranteed investment outcome.

Select Try the example in the form to load these values and calculate them again. This replaces the current form inputs. Compare the result with the method and worked explanation below.

The method, explained

Approximate doubling time = 72 ÷ annual percentage rate. The comparison uses exact annual compounding: ln(2) ÷ ln(1 + rate/100).

A WORKED EXAMPLE

At 8%, the rule gives 9 years; exact annual compounding gives about 9.006 years.

What to keep in mind

The rule is an approximation and becomes less accurate at extreme rates. Returns are assumed constant, positive and reinvested.

Common questions

Does this predict an investment return?

No. You supply the rate; the tool does not forecast performance or risk.

Why show an exact comparison?

It makes the approximation error visible for the particular rate you entered.

Methodology maintained by ClarityKit. How these tools are built and checked.