Rule of 72: The Fastest Way to Measure the Power of Time and Interest

October 19, 2025 | Kevin Brierton Team | ,

By Kevin Brierton | Your No Excuse Lender | Branch Manager NMLS 599873 | CMPS | CLA

Have you ever wondered how long it takes for your money to double?
The answer might be simpler—and more powerful—than you think.

In the Borrow Smart and Certified Liability Advisor programs, we teach that money is always moving. It’s either moving toward you or away from you. The Rule of 72 helps you measure which direction it’s headed—and how fast.

What is the Rule of 72?

The Rule of 72 is a simple formula to estimate how long it will take for money to double at a given rate of return.
You simply divide 72 by your rate of return to find out how many years it takes for your money to double.

Example:
If you earn 6%, your money doubles every 12 years (72 ÷ 6 = 12).
If you earn 12%, your money doubles every 6 years (72 ÷ 12 = 6).

This means time and rate of return are your two most powerful allies—or enemies—when building wealth.

The Flip Side: The Cost of Borrowing

Here’s where Borrow Smart and CLA thinking expand the conversation.
The Rule of 72 doesn’t just work for investments. It works against you with debt.

If you’re paying 12% interest on a credit card, your debt doubles every 6 years—if left unpaid.
So the same principle that can grow your money can also quietly erode it.

This is why we teach clients to manage the liability side of their balance sheet with the same discipline they apply to their investments. Every dollar lost to inefficient interest or poor structure is a dollar that could have been compounding for your future.

Borrow Smart | Repay Smart™

The Rule of 72 is more than a math shortcut—it’s a mindset shift.
When you understand how time and interest work together, you stop chasing rate and start building strategy.

For example:

  • Reducing non-deductible, high-interest debt frees cash flow that can be redirected toward compounding assets.
  • Choosing tax-efficient borrowing (like a well-structured mortgage or HELOC) can create liquidity for investment or protection strategies.
  • Measuring opportunity cost helps you see that every decision to “pay off” or “hold” debt carries a growth consequence—good or bad.

Why This Matters

The difference between earning 6% and 10% doesn’t just look small—it changes your entire future.

$100,000 at 6% doubles every 12 years:
After 36 years = $800,000

$100,000 at 10% doubles every 7.2 years:
After 36 years = $3.2 million

That’s the power of time, rate, and smart decisions compounding together.

The Bottom Line

Borrow Smart and CLA advisors don’t just talk about interest rates—they teach the laws of money.
We help clients see that the true cost of any decision isn’t measured in today’s rate, but in the lost opportunity for growth tomorrow.

So whether it’s your mortgage, your savings plan, or your overall financial strategy—remember the Rule of 72.

Time and interest don’t take days off.
Make sure they’re working for you, not against you.

Disclosure:
This information is for educational purposes only and should not be considered investment or financial advice. Always consult with a licensed financial advisor or tax professional before making investment decisions.