Are You Less Behind Than You Think?

Feeling Discouraged

Some people feel discouraged with their finances.

However, it’s not all doom and gloom!

Let’s say someone is 40 years old and has $200,000 saved for retirement.

Here’s where the “rule” of 72 comes in handy.

“Rule” of 72

It’s a way to determine about how long it takes an investment to double, given an annual growth rate.

Here’s how it works:

  • Divide 72 by the annual growth percentage.

  • The result is about how many years it takes to double.

"Rule" of 72 text. Annual growth rate of: 4% doubles in about 18 years (72 / 4); 6% doubles in about 12 years (72 / 12); 8% doubles in about 9 years (72 / 8); 12% doubles in about 6 years (72 / 12).

Exponential Growth

This is why saving early is so incredibly powerful.

However, exponential growth is notoriously difficult for us to get our heads wrapped around.

The “rule” of 72 helps us understand its power.

Guideline, Not Rule

However, the “rule” of 72 is more like a guideline than an actual rule. It’s a rough estimate and more accurate at 6-9% annual growth rates.

Consider an investment which had the great fortune to double in a year:

  • It didn’t take 0.72 years - that is, 72 / 100.

  • It took the whole year to double.

That’s almost a 39% error!

When It’s Most Accurate

The “rule” of 72’s error rate is lowest around 8% annual growth.

Above 19% annual growth, the error rate is over 5%.

Target on a hay bale. Inner yellow ring of 6-19% < 1% error,  next red ring of 4-12% growth < 2% growth, next blue ring of 2-14% growth < 3% error, next black ring of 1-16% growth < 4% error, next white ring of 17-18% growth < 5% error.

Limitations

Like many financial heuristics, the “rule” of 72 has real limitations.

I find it best to take the time to model growth accurately.

If you’re interested in a review of your situation, please…


Disclaimer

In addition to the usual disclaimers, neither this post nor this video includes any financial, tax, or legal advice.

Kevin Estes, CFP®, MBA | Founder | Scaled Finance

Kevin Estes is a financial planner helping T-Mobile employees and their families live their best lives.

He worked in T-Mobile Financial Planning & Analysis for nine years and has extensive experience with T-Mobile’s compensation and benefits package. He received a certificate in financial planning from Boston University, passed the CERTIFIED FINANCIAL PLANNER™ exam, and founded Scaled Financed in 2022.

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https://www.scaledfinance.com/
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