You want to know how long it will take you to double your money when it is invested at different interest rates. The amount of time it takes to double in value depends on the interest rate. To estimate the number of periods to double your investment use the "Rule of 72 " To calculate the "Rule of 72 " divide 0.72 by the interest rate. (Don't forget to include the decimal point) That tells you approximately how many periods it will take to double your money if interest is compounded "Compounded" means interest is paid on both the principal and any interest earned up to that point. It is larger every time. "Simple" interest is when the interest is paid only on the principal. It is a fixed amount. Let's test this theory for different interest rates Enter formulas in cells C19 C20 and C21 Copy the formulas into the range D19:K21 Rule of 72 calculation =0.72/ by the interest rate. This can be written as =072/0.03, for example. Rule of 72 calculation =.0;72 / by the interest rate. This can also be expressed in integers, =72/3 for example. Is the rule of 72 a reliable way to estimate doubling time? What is the trend in the "Amount of Savings" as interest rates increase? You want to know how long it will take you to double your money when it is invested at different interest rates. The amount of time it takes to double in value depends on the interest rate. To estimate the number of periods to double your investment use the "Rule of 72 " To calculate the "Rule of 72 " divide 0.72 by the interest rate. (Don't forget to include the decimal point) That tells you approximately how many periods it will take to double your money if interest is compounded "Compounded" means interest is paid on both the principal and any interest earned up to that point. It is larger every time. "Simple" interest is when the interest is paid only on the principal. It is a fixed amount. Let's test this theory for different interest rates Enter formulas in cells C19 C20 and C21 Copy the formulas into the range D19:K21 Rule of 72 calculation =0.72/ by the interest rate. This can be written as =072/0.03, for example. Rule of 72 calculation =.0;72 / by the interest rate. This can also be expressed in integers, =72/3 for example. Is the rule of 72 a reliable way to estimate doubling time? What is the trend in the "Amount of Savings" as interest rates increase