Rule of 72 Calculator

Use the Rule of 72 to estimate how many years it takes to double your investment at a given interest rate.

Estimate how long it takes to double your money.

About This Calculator

The Rule of 72 is a simple mental math shortcut to estimate how long it takes for an investment to double. Just divide 72 by your expected annual return rate.

How It Works

Years to Double = 72 ÷ Annual Interest Rate
  • At 6% return: 72 ÷ 6 = 12 years to double
  • At 9% return: 72 ÷ 9 = 8 years to double
  • At 12% return: 72 ÷ 12 = 6 years to double

For precise calculations, use our Compound Interest Calculator.

Frequently Asked Questions

How is Rule of 72 calculated?

Years to Double = 72 ÷ Annual Interest Rate. At 6%: 72÷6 = 12 years. At 8%: 72÷8 = 9 years. At 12%: 72÷12 = 6 years. Quick mental math for investing!

Why does the Rule of 72 work?

It's a mathematical approximation of compound interest formula ln(2)/ln(1+r). 72 is used because it's divisible by many numbers (2,3,4,6,8,9,12) making mental math easy.

Rule of 72 vs Rule of 70 which is better?

Rule of 70 is more accurate for rates under 10%. Rule of 72 is easier for mental math. For precise calculations, use actual compound interest formula.