Rule of 72 Calculator
Estimate how long it takes to double your money at a given interest rate. A quick mental math trick for investors.
Calculate Doubling Time
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Results
Years to Double
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Doubled Amount
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Exact Time
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The Rule of 72
The Rule of 72 is a simple formula to estimate doubling time:
Years to Double ≈ 72 ÷ Interest Rate
For example, at 8% interest: 72 ÷ 8 = 9 years to double your money.
Doubling Time at Common Rates
| Interest Rate | Years to Double | Example Investment |
|---|---|---|
| 2% | 36 years | Savings account |
| 4% | 18 years | Bonds |
| 6% | 12 years | Conservative portfolio |
| 8% | 9 years | Balanced portfolio |
| 10% | 7.2 years | Stock market average |
| 12% | 6 years | Growth portfolio |
The Power of Multiple Doublings
| Doubling | Years | Value |
|---|
How Accurate is the Rule of 72?
The Rule of 72 is most accurate for interest rates between 6% and 10%. For lower rates, use 70; for higher rates, use 73-75. The exact formula uses natural logarithms: Years = ln(2) ÷ ln(1 + r).
Related Rules
- Rule of 114: Triple your money (114 ÷ rate)
- Rule of 144: Quadruple your money (144 ÷ rate)