Divide 72 by your annual return to find how long it takes to double your money. See multiple doublings and the exact answer vs. the Rule of 72 estimate.
The Rule of 72 is a mental math shortcut accurate within 1–2% for rates between 2–20%. At 6%, money doubles in 72÷6 = 12 years. It also works in reverse: 72÷years = rate needed to double. Use it to instantly evaluate any investment, debt, or inflation scenario.