The Rule of 72 is a simple mathematical formula used to estimate the amount of time it will take for an investment to double in value, based on a given interest rate or rate of return. It works by dividing the number 72 by the interest rate or rate of return to determine the approximate number of years it will take for the investment to double. The origins of the Rule of 72 are not entirely clear, but it is believed to have been popularized by the Italian mathematician and economist Luca Pacioli in the early 16th century. However, the formula may have been used in various forms for many centuries before that. The Rule of 72 has been used by investors and financial professionals for centuries as a quick and easy way to estimate investment growth. It is a simple rule of thumb that can be applied to a wide range of investments and can help individuals make informed decisions about their financial goals.

To use the Rule of 72 to estimate the time it will take for an investment to double, you simply divide the number 72 by the annual interest rate or rate of return. The result will be the approximate number of years it will take for the investment to double in value.

For example, if an investment has an annual rate of return of 8%, you would divide 72 by 8, which equals 9. This means it would take approximately 9 years for the investment to double in value.

The formula is expressed as:

Years to double = 72 / Annual interest rate or rate of return

It is important to note that the Rule of 72 is an estimation and assumes that the interest rate or rate of return remains constant over the period of time being considered. It may not be accurate for investments with highly variable returns or for longer time periods.

To use the Rule of 72, follow these steps:

Determine the annual interest rate or rate of return of your investment.

Divide the number 72 by the annual interest rate or rate of return.

The result will be the approximate number of years it will take for the investment to double in value.

For example, if your investment has an annual interest rate of 6%, you would divide 72 by 6 to get 12. This means it would take approximately 12 years for the investment to double in value.

Alternatively, if you want to know what interest rate or rate of return is needed to double your investment in a certain amount of time, you can rearrange the formula to calculate the required rate of return. For example, if you want your investment to double in 8 years, you would divide 72 by 8 to get 9, which means you would need an annual interest rate of approximately 9% to double your investment in 8 years.

Remember, the Rule of 72 is an estimation and assumes that the interest rate or rate of return remains constant over the period of time being considered. It is a quick and easy way to estimate investment growth, but it may not be entirely accurate in all situations.