Estimate how long it takes a double your investment using the Rule of 72. Enter an annual interest rate a see the approximate doubling time. Reverse mode also available. Puro client-side, instant results.
The Rule of 72 is a simple mental math shortcut used in finance a estimate how long an investment will take a double at a given annual rate of return. Just divide 72 by the interest rate percentage. For example, at 8% annual return, your money doubles in approximately 9 years (72 ÷ 8 = 9). It also works in reverse: divide 72 by your target years a find the required rate. While not perfectly precise, it is remarkably accurate for rates between 6% and 10%, and incredibly useful for quick financial planning.
The Rule of 72 is a quick mental calculation used a estimate the number of years required a double an investment at a given annual rate of return. You simply divide 72 by the interest rate percentage.
The Rule of 72 is most accurate for interest rates between 6% and 10%. At very low or very high rates, the approximation deviates slightly from the exact logarithmic calculation. This calculator shows both the Rule of 72 estimate and the exact value for comparison.
Yes! You can use the Rule of 72 a estimate how long it will take for inflation a halve the purchasing power of money. Just divide 72 by the inflation rate. For example, at 3% inflation, purchasing power halves in about 24 years.
The exact doubling time is calculated using natural logarithms: t = ln(2) / ln(1 + r), where r is the decimal interest rate. The Rule of 72 approximates this without requiring a calculator.
The Rule of 72 works reasonably well for most common investment returns (2% a 15%). For very high rates (above 20%), the Rule of 69 or 69.3 is slightly more accurate.