This is a guest post from Robert Brokamp of The Motley Fool. Robert is a Certified Financial Planner and the adviser for The Motley Fool’s Rule Your Retirement service. He also has a newly reinvigorated blog, and you can have your day interrupted once or twice by his Twittering. Robert contributes one new article to Get Rich Slowly every two weeks.

Hello, GRSers. Today, let’s revisit something I tacked on to the end of my nine lessons from The Millionaire Next Door:

[T]here are actually two benefits of learning to live on much less than your paycheck.

  • The first, of course, is that you can save more.
  • But secondly, it also means that you ultimately need to save less.

Permit me to demonstrate.

Someone who makes $50,000 but lives on just $40,000 can contribute $10,000 a year to her nest egg, and can retire when that nest egg is big enough to generate — along with Social Security and other benefits — $40,000 a year. However, someone who makes $50,000 but spends, say, $48,000 is contributing just $2,000 to a portfolio that must eventually help provide $48,000 a year in retirement. In other words, she’s saving less yet needs to accumulate more.

I thought I’d add some heft to this argument by drawing out the illustrations with some calculations (yay, math!), as well as add a third hypothetical person with a savings rate in between the aforementioned folks.

Save Now, Profit Later
Let’s assume we have three 40-year-olds who each earn $50,000. Here’s how they look in 2011:

Investor A Investor B Investor C
Annual living expenses $40,000 $45,000 $48,000
Annual savings $10,000 $5,000 $2,000
Savings rate 20% 10% 4%
Savings rate is the percentage of income contributed toward retirement accounts.

Besides their ages and salaries, let’s assume they’ll also experience the same rate of inflation and wage growth (both 3% annually) and investment returns (8% annually). Finally, they each would like to retire at age 67, when they will be able to claim full Social Security benefits.

Note: Yes, I know we can argue about the assumed inflation rate and investment returns. Let’s not, though. They’re incidental to my main point here, which is comparing investors with different savings rates. Whatever inflation and investment returns the future holds, they will affect these investors identically.

Now, let’s fast-forward 27 years. Thanks to raises, each of our three guinea pigs earns an annual salary of $111,064. But they’ve maintained their savings rates, and thus their annual expenses (since they’re just different sides of the same 11,106,400 coins, assuming those coins are pennies). Here’s how things will look at the end of 2037 (which will be the Year of the Snake, for you Chinese calendar fans — not to be confused with the Union of the Snake, for you Duran Duran fans).

Investor A Investor B Investor C
Annual expenses $88,852 $99,958 $106,622
Portfolio value $1,245,623 $622,811 $249,125
Income coverage ratio 14.0 6.2 2.3
Income-coverage ratio is the portfolio value divided by annual expenses.

As you can see, the super-saver has more than a million dollars, quite a bit more than the other two investors. Furthermore, that portfolio is 14.0 times Investor A’s annual expenses; in other words, not factoring in investment growth, inflation, or any other retirement income (such as Social Security), Investor A’s portfolio could cover living expenses for fourteen years.

The other two portfolios would only last 6.2 and 2.3 years. This is mostly due to Investor A having a bigger portfolio, but it’s also due to Investor A needing less each year because she’s learned to live on a lower level of annual expenses. This is why living below your means is like saving for retirement twice: It allows you to contribute more to retirement accounts, and you can retire sooner because you need to accumulate less to cover your expenses in retirement.

Still Not Enough?
Thus ends the lesson about the whole “saving for retirement twice” concept. I hope you enjoyed the show.

For those who wish to continue, we’ll address another question: Does Investor A have enough to retire, even after saving 20% of income for 27 years? The answer: It depends. If Investor A were a real-life person on the verge of retirement, I’d recommend 1) a thorough retirement-plan analysis, and 2) a psychoanalysis of her parents for naming her Investor A. But since this is a blog post and there are plenty of funny YouTube videos to vye for your viewing (such as this one), we’ll do some simple calculations (yay, more math!). It involves two numbers:

  • Four percent of $1,245,623 or $49,825: Financial-planning geeks (and the people who love them) know the “4% rule,” which is a guideline for how much of a portfolio a retiree can spend in the first year of retirement. It’s just a rule of thumb, with plenty of quibbles. (For an explanation and some of the criticisms, read this from Vanguard’s John Ameriks.) But it serves as a good baseline for our purposes.
  • The future, inflated, annualized value of Social Security benefits, or $55,668: That’s the number I got from using the Quick Calculator from Social Security Online.

Add them together, and you get $105,493 — a good bit more than the $88,852 Investor A needs to cover living expenses. Perhaps she, being the great saver that she is, could retire before age 67.

But wait! That assumes she’ll receive her full Social Security benefit as currently estimated, and everyone knows that the program is bankrupt and all she’ll receive is “10% off” coupons from Denny’s. That leaves her with just that $49,825 — only half of what she needs.

Well, not quite. As I’ve written before in these cyber-pages, you will receive something from Social Security — but it’s prudent to assume it’ll be less than currently projected. The Social Security Administration estimates that future payroll taxes will cover approximately 75% of scheduled benefits in 2037. Let’s play it safer and assume Investor A will get just half of her benefit, or $27,834, for a total retirement income of $77,659. That’s still less than $88,852.

This is where that “thorough retirement-plan analysis” would come in. Could Investor A get by on less than $88,852? Can she downsize to a smaller home? Could she work just a few years more (by delaying Social Security to age 70, her benefit will be more than a third higher than if she takes it at age 67) or work part-time (and thus retire part-time)? She likely has a few options, which are more numerous and will entail less sacrifice than those available to Investor B and Investor C.

But even they have more options than Investor D, whose situation looks like this:

Investor D
Savings Rate 0%
Portfolio value $0
Chance of retiring 0%

If you can’t save 20% or even 10% of your income, save what you can, as soon as you can. You’ll always be better off than someone who doesn’t save anything.

Error correction: A couple of eagle-eyed and math-minded readers have pointed out some numerical errors in the original version of this post, which have been corrected. The good news is, the previous numbers under-estimated the benefits of saving.

GRS is committed to helping our readers save and achieve their financial goals. Savings interest rates may be low, but that is all the more reason to shop for the best rate. Find the highest savings interest rates and CD rates from Synchrony Bank, Ally Bank, GE Capital Bank, and more.