Calculyn

Rule of 72 Calculator

Find how many years it takes money to double at a given return — or the return needed to double in a set time.

Results update as you type.

Years to double (exact)

9years
Rule of 72 estimate
9years
Years to triple
14.3years
Doubled amount
$20,000
Years to double (exact)9

Results are estimates for planning and are not financial advice.

Was this calculator helpful?

Quick answer

At 8% a year, money doubles in about 9 years (exactly 9.0).

How it works

The Rule of 72 is a quick mental shortcut: divide 72 by your yearly return to estimate how long money takes to double. We also show the exact answer.

Formula

Estimate = 72 ÷ rate · Exact = ln(2) ÷ ln(1 + rate)

Assumptions & limitations

  • Results are rounded for display.

Frequently asked questions

How accurate is the Rule of 72?

Very close for returns between about 6% and 10%. It drifts at very low or very high rates.