How long does your investment need to double or triple its value?

Recently I come across an interesting formula of mathematic which people use it to calculate the amount of time they needed to double the value of their investment. The mathematic formula is “The Rule of 72”.

Suppose you bought an investment which is said to return you 10% each year. You can calculate by using the number 72 divide by the percentage.

For example: 10 / 72 = 7.2 . The answer is 7.2 year.


If your investment give interest at only 5% each year,

72 / 5 = 14.4 year.


When you need to know how long does your investment need to triple its value, use the “Rule of 115”

115 / 9 = 12.7 year

These same rules can be use to count for inflation. If your country are having inflation of 9%. 72 divide by 9 = 8 year. This means that in another 8 year, the inflation will be double.

How long it take to double your investment
72 / your interest rate = how long it will take

How long it take to triple your investment
115/ your interest rate = how long it take