Rule of 72

Definition

The Rule of 72 is a simple mathematical rule used to estimate the time required for a given investment or account to double in value at a certain interest rate. It provides a quick and easy way to calculate the approximate doubling time of an investment or account balance.

5 Must Know Facts For Your Next Test

1. The Rule of 72 is a quick way to estimate the doubling time of an investment or account balance by dividing 72 by the annual interest rate.
2. The Rule of 72 is particularly useful for simple interest calculations, where the interest earned is not compounded over time.
3. The Rule of 72 provides an approximate result, as the actual doubling time may vary slightly depending on the compounding frequency and other factors.
4. The Rule of 72 can be used to compare the growth potential of different investment options or to determine how long it will take to reach a financial goal.
5. The Rule of 72 is a valuable tool for personal finance and investment planning, as it allows individuals to quickly estimate the potential growth of their savings or investments.

Review Questions

• Explain how the Rule of 72 can be used to solve simple interest applications.
  • The Rule of 72 can be used to quickly estimate the doubling time of an investment or account balance that earns simple interest. By dividing 72 by the annual interest rate, you can determine the approximate number of years it will take for the principal to double in value. This is particularly useful in simple interest applications, where the interest earned is not compounded over time. For example, if an investment earns 6% simple interest per year, the Rule of 72 suggests it will take approximately 12 years (72 ÷ 6 = 12) for the principal to double in value.
• Describe how the Rule of 72 differs from the concept of compound interest.
  • The Rule of 72 is primarily used for simple interest calculations, where the interest earned is not compounded over time. In contrast, compound interest is the interest earned on interest, where the interest earned in each period is added to the principal, and the total amount earns interest in the next period. While the Rule of 72 provides a quick estimate of the doubling time for simple interest, it does not account for the exponential growth associated with compound interest. The actual doubling time for an investment or account earning compound interest may be different from the estimate provided by the Rule of 72, especially as the interest rate or compounding frequency changes.
• Analyze how the Rule of 72 can be used to compare the growth potential of different investment options in the context of simple interest applications.
  • The Rule of 72 can be a valuable tool for comparing the growth potential of different investment options in the context of simple interest applications. By dividing 72 by the annual interest rate of each investment, you can quickly estimate the doubling time for each option and compare them. This allows you to assess which investment has the potential to double your money the fastest, given the same initial principal and time frame. For example, if one investment earns 4% simple interest per year and another earns 8% simple interest per year, the Rule of 72 suggests the 8% investment will double in value in approximately 9 years (72 ÷ 8 = 9), while the 4% investment will take around 18 years (72 ÷ 4 = 18) to double. This information can help you make more informed decisions about where to allocate your savings or investments based on your financial goals and risk tolerance.

Related terms

Simple Interest:

Simple interest is a method of calculating the interest earned on an investment or loan, where the interest is calculated based on the principal amount and the interest rate, without compounding over time.

Compound Interest:

Compound interest is the interest earned on interest, where the interest earned in each period is added to the principal, and the total amount earns interest in the next period.

Doubling Time: Doubling time is the amount of time it takes for an investment or account balance to double in value, given a specific interest rate.