Rule of 69.3

The third rule for calculating the time period to double an investment is the Rule of 69.3. Unlike Rule of 72 and Rule of 70, the factor in Rule of 69.3 is the annual interest rate.

The formula for this rule is to divide the number 69.3 by the annual interest rate (assuming it is raised continuously) expressed as a percentage. This proves the Rule of 69.3 for continuously compounded interest.

It is important to note that the Rule of 69.3 is an approximate calculation and not an exact forecast. Keep in mind that several other factors, such as taxes and inflation, can also affect investments.