Which concept estimates the time required for an investment to double at a given interest rate by dividing 72 by the rate?

Which concept estimates the time required for an investment to double at a given interest rate by dividing 72 by the rate?

• A. Revenues
• B. Social Entrepreneurship
• C. Rule of 72
• D. Short-Term Debt

Answer: (C)

The idea here is a quick way to estimate how long it takes for money to double under compound interest: the Rule of 72. You take the annual interest rate (as a percent) and divide 72 by that rate to get the approximate number of years needed for the investment to double. This works because, for typical rates, the logarithmic growth that drives doubling can be approximated with a simple division, and 72 is a convenient number that makes mental math close to the exact result. For example, at an 8% rate, the Rule of 72 gives about 9 years to double. The precise calculation using the full formula t = ln(2) / ln(1 + 0.08) yields about 9.01 years, so the shortcut is very close. The Rule of 72 is most reliable for moderate rates and is less precise at very high or very low rates, where the exact formula should be used.

The idea here is a quick way to estimate how long it takes for money to double under compound interest: the Rule of 72. You take the annual interest rate (as a percent) and divide 72 by that rate to get the approximate number of years needed for the investment to double. This works because, for typical rates, the logarithmic growth that drives doubling can be approximated with a simple division, and 72 is a convenient number that makes mental math close to the exact result.

For example, at an 8% rate, the Rule of 72 gives about 9 years to double. The precise calculation using the full formula t = ln(2) / ln(1 + 0.08) yields about 9.01 years, so the shortcut is very close. The Rule of 72 is most reliable for moderate rates and is less precise at very high or very low rates, where the exact formula should be used.