Estimate doubling time with the rule of 72
How long until money doubles? Divide 72 by the yearly percentage.
- Take the yearly growth rate as a whole number, like 6 for 6%.
- Divide 72 by it: 72 ÷ 6 = 12 years to double.
- It works for debt too: at 24% interest, a balance you never pay down doubles in about 3 years.
Tip: It's an approximation that's closest for rates between about 6% and 10%.
Try it now: How long does money take to double at 8%? At 4%? (9 years and 18 years.)