What Is the Rule of 72?

I’m going to start sprinkling in some simple financial concepts that can actually be useful in real life.

Up this week: The Rule of 72.

Ever wondered how long it will take to double your money?

Good news, you don’t need a calculator or a spreadsheet. There’s a quick shortcut:

$\text{Years to Double} = \frac{72}{\text{Rate of Return}}$

That’s it.

Take 72 and divide it by your expected rate of return, and you’ll get a rough estimate of how many years it takes to double your money.

How to Use It

You can use the Rule of 72 in two ways:

1. How long will it take to double your money?

Divide 72 by your expected return
Example:
- 10% return → 72 ÷ 10 = 7.2 years

2. What return do you need to double your money in a certain time?

Divide 72 by the number of years
Example:
- Want to double in 5 years → 72 ÷ 5 = 14.4% return

It’s Not Just for Investing

This concept works anywhere there’s compounding, not just investments.

💳 Debt

An 18% interest rate?
Your balance could double in about 4 years if nothing is paid down

💸 Inflation

At 3% inflation:
Your purchasing power gets cut in half in about 24 years

That one hits a little different.

Can You Use It for Months or Quarters?

Yes but keep it consistent.

If you’re using monthly growth rates, your answer will come out in months.

Example:
- 1.2% monthly growth → 72 ÷ 1.2 = 60 months (5 years)

How Accurate Is It?

The Rule of 72 is a shortcut, not a precision tool.

Works best between 6% and 10%
Still useful outside that range, just a little less precise

If you want to get fancy:

For higher rates, you can bump 72 up slightly
For lower rates, bring it down a bit

But in most cases, you’re splitting hairs.

Why This Matters

This isn’t just a fun math trick.

It helps you:

Understand how powerful compounding really is
See how damaging high-interest debt can be
Visualize the long-term impact of inflation

Final Thought

Tuck this one away.

Next time someone says, “My investments will never double,”
just ask them their rate of return.

If your reaction is, “That’s all?”…
you might have a follow-up conversation worth having.

Financial Concepts: What Is the Rule of 72?