What Is the Rule of 72?

Investing can be a complex world, filled with jargon and formulas that might seem intimidating at first glance. But fear not, because there’s a handy rule called the Rule of 72 that can help you estimate how long it will take for your investments to double, without needing a math degree!

What is the Rule of 72?

Imagine you have some money invested and you’re curious about when it will double in value. The Rule of 72 is a simple trick to give you a rough estimate. Just divide 72 by the annual rate of return you expect, and you’ll get an approximate number of years it will take for your investment to double.

How to Use the Rule of 72

Let’s break it down with an example: say you have $10,000 invested with an annual return of 8%. Divide 72 by 8, and you get 9. So, roughly speaking, it would take around 9 years for your $10,000 investment to become $20,000.

When to Use the Rule of 72

This rule isn’t perfect, though. It works best for fixed rates of return, and it’s most accurate for rates between 6% and 10%. If you’re dealing with rates outside of that range, or you want a more precise calculation, you might consider using other methods.

A Closer Look

For those who want a bit more accuracy, there’s a fancy logarithmic formula you can use. It involves natural logarithms and complicated math stuff, but basically, it gives you a more precise estimate of when your investment will double.


The Rule of 72 is a handy tool for getting a quick estimate of how long it will take for your investments to double. While it’s not perfect, it can give you a good starting point for your financial planning. Remember though, it’s just a rule of thumb, so always do your research and consult with a financial advisor for personalized advice.


1. Is the Rule of 72 always accurate?

The Rule of 72 works best for fixed rates of return between 6% and 10%. Outside of this range, or for more precise calculations, you might need to use other methods.

2. Can I use the Rule of 72 for any investment?

It’s best suited for investments with a fixed rate of return and no additional contributions. For more complex investments, you might need to consider other factors.

3. How can I calculate compound interest using the Rule of 72?

You can reverse the calculation to estimate the annual compound interest rate by dividing 72 by the number of years it took for your investment to double. For example, if it took 8 years to double, the annual compound interest rate would be approximately 9%.

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