Investing Basics

What Is the Rule of 72?

The rule of 72 is a quick way to estimate how many years it takes for a value to double at a given annual compound growth rate: divide 72 by the rate. At 8% a year, a value doubles in roughly 72 ÷ 8 = 9 years. It works best for rates between about 6% and 10%.

Formula

Years to double ≈ 72 ÷ annual rate (in percent). It can also be reversed: rate needed to double in a given time ≈ 72 ÷ years.

Using It for Inflation or Debt

The same shortcut estimates how fast prices double under inflation, or how fast an unpaid debt balance doubles at a given interest rate.

How Accurate It Is

The exact doubling time is ln(2) ÷ ln(1 + r). The rule of 72 is an approximation that becomes less accurate at very low or very high rates.

🧮 Calculate It Yourself

Put Rule of 72 into practice with these free calculators — no sign-up, nothing stored.

⏳ Rule of 72 Calculator A quick shortcut for estimating how fast your money doubles. Calculate → 📈 Compound Interest Calculator See how your money grows with compound interest and regular monthly contributions. Calculate → 🎈 Inflation Calculator Future cost and buying power of money for any inflation rate. Calculate →

🔗 Related Terms

Compound Interest Compound Annual Growth Rate (CAGR) Inflation

More Investing Basics Terms

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Last updated: September 27, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.