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Rule of 72 Calculator

How long to double your investment

Rule of 72

Estimate how many years it takes to double an investment.

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The Rule of 72 is a simple mental math shortcut to estimate how long it takes an investment to double, or what growth rate is needed to double in a given time. Divide 72 by the annual return rate to get years to double.

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Tip: Use Rule of 115 to estimate tripling time: 115 / rate. Use Rule of 144 for quadrupling: 144 / rate.

  1. 1Years to double = 72 / Annual Interest Rate (%)
  2. 2Rate needed to double = 72 / Number of years
  3. 3Works best for rates between 6% and 10% (±1 year accuracy)
  4. 4For continuous compounding, use 69.3 instead of 72
8% annual return=Doubles in ~9 years (72/8)Actual: 9.01 years
Want to double in 6 years=Need ~12% return (72/6)Actual rate: 12.25%
Annual RateYears to DoubleActual Years
2%36 years35.0
3%24 years23.4
6%12 years11.9
8%9 years9.0
10%7.2 years7.3
12%6 years6.1
18%4 years4.2
72%1 year1.3

Fun Fact

The Rule of 72 also works in reverse for debt. At 18% credit card interest, your debt doubles in just 4 years if you make no payments. At 24% payday loan rates, it doubles in 3 years.

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