Rule of 72 Calculator
Use the Rule of 72 to quickly estimate how long it takes to double your money at any interest rate.
Before you calculate
This is an approximation for positive constant returns. Accuracy changes with the rate; use the exact comparison for a precise doubling time.
The Rule of 72
The Rule of 72 is a simple mental math shortcut: divide 72 by the annual rate of return to estimate how long it takes an investment to double. The exact answer uses the natural log formula: t = ln(2) / ln(1 + r).
Years to Double ≈ 72 / Annual Rate (%)Example Scenarios
Stock Market Returns
The historical average stock market return is roughly 7–10% per year. At 8%, the Rule of 72 estimates your portfolio doubles in about 9 years. At 10%, it doubles in 7.2 years.
High-Interest Debt
Credit card debt at 24% APR will double in just 3 years if left unpaid. The Rule of 72 makes this visceral — what works for investments works against you with debt.
Sources & calculation notes
Maintained by MoneyCalc. Results are estimates based on the inputs and assumptions shown, not personalized financial advice or a lender quote. Default rates are examples unless a specific tax year or official table is identified.
References explain the underlying concepts or rules. They do not endorse or independently certify this implementation.
Calculations run in your browser. Some tools retain settings on this device. Displayed rounding can produce small differences from a statement or contract.