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Results are estimates only and should not be considered financial or medical advice. Always consult a qualified professional.

  1. Home
  2. /Rule of 72 Calculator

Rule of 72 Calculator

Estimate how long it takes an investment to double at a given return, or the rate you need to double your money by a target date.

%
yrs

Results

Years to Double (Rule of 72)

10.3 yrs

Years to Double (Exact)

10.2 yrs

difference 0.04

Rate Needed to Double in Specified Time

7.2%

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Doubling Time by Return Rate

RateRule of 72 (years)Exact (years)
1%72.069.7
2%36.035.0
3%24.023.4
4%18.017.7
5%14.414.2
6%12.011.9
7%10.310.2
8%9.09.0
9%8.08.0
10%7.27.3
12%6.06.1
15%4.85.0
20%3.63.8

The Rule of 72 stays within a few months of the exact doubling time for rates between 6% and 10%.

Results are estimates only and should not be considered financial advice. Always consult a qualified professional before making financial decisions.

Formula

Years to double ≈ 72 ÷ Annual Return %

Worked Example

At 7% annual return: 72 ÷ 7 ≈ 10.3 years to double. With the exact formula, doubling at 7% takes about 10.2 years — the rule is remarkably close.

Frequently Asked Questions

What is the Rule of 72?
The Rule of 72 is a shortcut: divide 72 by your annual return percentage to estimate how many years it takes your money to double. At 7% per year, money doubles in about 72 ÷ 7 ≈ 10.3 years.
How accurate is the Rule of 72?
It is very accurate for rates between 6% and 10%, which is where most investors operate. At very high or very low rates the estimate drifts slightly, but it remains a useful mental shortcut.
Where does the 72 come from?
The rule comes from the mathematics of logarithms: ln(2) ÷ ln(1 + r) gives the exact doubling time, and 72 is the round number that makes r × years ≈ 72 a close approximation across common rates.
What rate do I need to double my money in a specific time?
Divide 72 by the number of years. To double in 8 years you need about 72 ÷ 8 = 9% per year. Higher expected returns usually mean more risk, which the rule doesn't capture.
Does the Rule of 72 work for debt too?
Yes. The same math applies whenever something grows at a compound rate — including the balance on a debt with compounding interest. A 24% APR credit card doubles a balance in about 3 years.
Does the Rule of 72 include contributions or withdrawals?
No. It assumes a single lump sum compounding with no additions or withdrawals. For regular contributions, use a compound savings or savings goal calculator instead.

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Compound Interest CalculatorCAGR CalculatorCompound Savings Calculator

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