Use the return after recurring fees.
%
$
Doubling Time
—
At your current return
Triple (Rule of 114)
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Quadruple (Rule of 144)
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Growth Over Time
Rule of 72 Result — Financial Depth
financialdepth.com/rule-of-72
Quick Summary (TL;DR)
- Years to double ≈ 72 ÷ your annual return. At 8% → ~9 years; at 12% → ~6.
- Triple uses 114 ÷ rate; quadruple uses 144 ÷ rate.
- Most accurate for 6–10% returns — use real returns for purchasing power.
- Formula:
Years ≈ 72 ÷ Rate(%)
How the Rule of 72 Works
The Rule of 72 is a shortcut for compound growth. Divide 72 by your annual rate of return and you get the approximate number of years for an investment to double. At 8% a year, money doubles in about 9 years; at 12%, in about 6. It works because of the math of compounding, and it is remarkably accurate for the 6–10% range most investors care about.
The same idea scales: divide 114 by your return to estimate a tripling, or 144 to estimate a quadrupling. These are mental-math estimates — the chart on this page shows the exact compounding for comparison. For continuous compounding, purists use 69.3 instead of 72, but 72 divides cleanly by more numbers, which is why it stuck.
Frequently Asked Questions
What is the Rule of 72?+
It is a quick way to estimate how long an investment takes to double: divide 72 by the annual return percentage. At 9%, money doubles in about 8 years.
How accurate is the Rule of 72?+
Very accurate for returns between about 6% and 10%. Outside that range it drifts slightly, so use exact compounding (shown in the chart) for precision.
How do I estimate tripling or quadrupling?+
Use the Rule of 114 for tripling and the Rule of 144 for quadrupling — same idea, divide the number by your annual return.
Key Considerations
- It’s an approximation, not exact. The Rule of 72 is most accurate around 8%. At very low or very high rates it drifts — use the chart for precise figures.
- Use real returns for planning. A 10% nominal return doubles your money in ~7 years, but after 3% inflation your purchasing power doubles closer to every 10 years.
- Fees compound too. A 1% annual fee doesn’t sound like much, but over decades it meaningfully lengthens your doubling time — plug your net-of-fee return in.
Related Tools
Decision guide
Know when the Rule of 72 is close—and when it is not
Dividing 72 by an annual rate gives a fast doubling-time estimate. It works best for moderate positive rates and becomes less precise at very low or high returns.
Exact doubling time reveals approximation error.
Divide 72 by available years to estimate a required rate.
What this model includes
- Rule-of-72 estimate and exact doubling time
- Quick comparisons across rates
What to add outside the model
- Contributions, withdrawals, taxes, and volatility
- Whether the return is realistic for the risk
Calculation standard: Formula details, source policy, tests, and limitations are documented in the FinancialDepth methodology. Reviewed July 18, 2026.