Rule of 72: The One-Second Math Trick That Tells You When Your Money Doubles

# Rule of 72: The One-Second Math Trick That Tells You When Your Money Doubles

> **Quick answer:** Divide 72 by your annual return rate and you get the number of years until your money doubles. At the S&P 500's historical 10% average: 7.2 years. At a 5% HYSA: 14.4 years. At 22% credit card APR: 3.3 years — but now it's working against you. The Rule of 72 is the single most useful number in personal finance, and it takes one second to use.

*This article is for informational purposes only and does not constitute financial advice. Consult a qualified financial advisor for personal financial decisions.*

Every finance concept you will ever learn — compound interest, inflation, debt, retirement math — ultimately comes down to one question: how fast does this number grow? The Rule of 72 answers that question instantly, without a spreadsheet, without a calculator app, without a finance degree. It is the mental math shortcut that Einsteins of investing use in the shower, and most people have never heard of it.

## What Is the Rule of 72?

The Rule of 72 is a simple formula: divide 72 by an annual rate of return (expressed as a whole number, not a decimal) and you get the approximate number of years it takes for an investment to double in value.