How long could it take to double your money?
If you're saving for college, retirement, or a large purchase, it can be useful to quickly calculate how an anticipated annual rate of return will affect your money over time. To find out, you can use a mathematical concept known as the Rule of 72. This rule can give you a close approximation of how long it would take for your money to double at any given rate of return, assuming annual compounding.
To use this rule, you simply divide 72 by your anticipated annual rate of return. The result is the approximate number of years it will take for your money to double.
For example, if your anticipated annual rate of return is 6%, you would divide 72 by 6. Your money can be expected to double in about 12 years. But if your anticipated annual rate of return is 8%, then your money can be expected to double in about 9 years.
The Rule of 72 can also be used to determine what rate of return you would need to double your money in a certain number of years. For example, if you have 12 years to double your money, then dividing 72 by 12 would tell you that you would need a rate of return of 6%.
Another way to use the Rule of 72 is to determine when something will be halved instead of doubled. For example, if you would like to estimate how long it would take for annual inflation to eat into your savings, you could divide 72 by the rate of inflation. For example, if inflation is 3%, then it would take 24 years for your money to be worth half its current value. If inflation jumped to 4%, then it would take only 18 years for your purchasing power to be halved.
Although using a calculator will give you more precise results, the Rule of 72 is a useful shortcut that can help you understand how long it might take to reach a financial goal, and what annual rate of return you might need to get there.