Doubling Time (Rule of 72)

"How long does it take my money to double — and how many doubles do I have left?"

Divide 72 by your annual rate of return and you get the approximate number of years it takes for your money to double.

— Debugging Your Personal Finance, Chapter 7

Expected real return (%)

The Rule of 72 is an approximation derived from the natural log of 2 (≈ 0.693). The "exact" multiplier above uses $(1+r)^t$ for the actual answer.

From Chapter 7 of Debugging Your Personal Finance. Simple calculator · Inputs stay in your browser · Not financial advice.