The Rule of 72 and Other Financial Hacks to Double Money

How to Do Investment Math in Your Head

If an agent tells you an investment will double your money in 8 years, is that a good deal? What interest rate are they actually offering? You don't need a spreadsheet to figure this out. By using a few simple mental math hacks, you can estimate compound interest growth in your head in seconds.

The Magic of the Rule of 72

The Rule of 72 is the most famous financial shortcut. To find out how many years it will take to double your money, divide 72 by the annual interest rate.

For example, if you invest in a mutual fund earning 12% annual returns, your money will double in approximately 6 years (72 / 12).

You can also use it in reverse: if you want your money to double in 8 years, you need an interest rate of 9% (72 / 8). It is incredibly handy during sales pitches.

Rules of 114 and 144: Tripling and Quadrupling

Want to know how long it takes to triple or quadruple your capital? Use the same math with different numbers:

Rule of 114 (Tripling): Divide 114 by your interest rate. At 10% interest, your money triples in 11.4 years.

Rule of 144 (Quadrupling): Divide 144 by your interest rate. At 12% interest, your money quadruples in 12 years. These quick rules help you bypass marketing jargon and compare options instantly.