The Rule of 72

The Rule of 72 isn’t exactly a secret formula. It’s more like a general rule. Usually, people use this rule to figure out how long it will take for some investment or savings account to double in value. The Rule of 72 is a cool little trick, however, and it has several useful applications for businesspeople.

What the rule says is that if you divide the value 72 by an interest rate percentage, your result is approximately the number of years it will take to double your money. For example, if you can stick money into some investment that pays 12 percent interest, it will take roughly six years to double your money because 72 / 12 = 6.

The Rule of 72 isn’t exact, but it’s usually close enough for government work. For example, if you invest $1,000 for 6 years at 12 percent interest, what you really get after 6 years isn’t $2,000 but $1,973.92.

If you’re in business, you can use the Rule of 72 for a couple of other forecasts, too:

To forecast how long it will take inflation to double the price of an item, divide 72 by the inflation rate. For example, if you own a building with a value that you figure will at least keep up with inflation, and you wonder how long the building will take to double in value if inflation runs at 4 percent, you just divide 72 by 4. The result is 18, meaning that it will take roughly 18 years for the building to double in value. Again, the Rule ...

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