Financial Calculators

Rule of 72 Calculator

Estimate how long an investment takes to double, and see how close the rule of 72 is to the exact answer.

Every figure below is labelled in the currency you pick. Amounts are not converted — enter values in the same currency.

%
$
Years to double
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What makes up the totalprincipalinterestfeesChange one input and watch which block moves. That is usually more useful than the total itself.

Why 72 and not 69.3

The mathematically exact numerator is 69.3 (100 × ln 2), which is right for continuous compounding. Seventy-two is used instead because it divides cleanly by 2, 3, 4, 6, 8, 9 and 12, and because it is more accurate in the 6–10% range where most people actually invest. The error is under half a year across that band.

The formula

Years ≈ 72 ÷ annual return %

Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.

How to use the Rule of 72 Calculator

  1. Fill in each field with your own figures — the defaults are only there as an example.
  2. The result updates as you type, so there is no button to press.
  3. Check the breakdown under the main result for the supporting numbers.
  4. Use the copy button to take the result with you, or share the link to reload the same inputs.

Rule of 72 Calculator — frequently asked questions

Is this rule of 72 calculator free to use?

Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.

How accurate is the result?

The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.

Can I use it on my phone?

Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.

What people search for

This page answers each of these searches. They are the exact phrases visitors use to find the rule of 72 calculator.

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About this calculator

Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.

Last reviewed August 19, 2026 · Calculation runs client-side · No data collected · Report an error