Rule of 72

The Rule of 72 Calculator provides a quick mental-math shortcut for estimating how long it takes an investment to double in value. Simply divide 72 by the annual return rate to get the approximate doubling time in years. This calculator goes beyond the basic rule by showing successive doubling periods — when your money becomes 2x, 4x, 8x, and 16x the original amount. It also compares the Rule of 72 estimate against the exact mathematical result so you can see the approximation error. The Rule of 72 is widely used by financial advisors and investors as a quick sanity check. At 8% annual returns money doubles roughly every 9 years, at 12% every 6 years. Understanding this helps you set realistic long-term expectations.