The Secret Math Behind Early Retirement

Early retirement often seems impossible. It's difficult enough these days to retire at age 65, so the thought of retiring early is a pipe dream for most people. Yet somehow this dream has become a reality for some diligent savers. In extreme cases, a few people have retired at an age when most of us are just getting started.

One well-known example is the man behind MrMoneyMustache.com, who retired at age 30 after just nine years of working. While he is the exception to the rule, he thinks that should change. He views early retirement as something most people can attain.

To understand how it works, let's take a look at the math behind early retirement. These numbers have implications for all retirees, not just those looking for an early exit.

So even if you think you're too late for early retirement, these strategies will still improve your retirement finances.

The math. How quickly you can retire depends on how much you can save. If you are able to save the often-recommended 15 percent of your take home pay, it will take about 45 years to retire. This conclusion assumes investments earn a real return (after inflation) of 5 percent, and that you live off of 4 percent of your nest egg once you do retire.

Now let's say you are a frugal and committed saver. If you are able to save 30 percent of your take home pay, your working years fall to about 30. At 40 percent the necessary work years before retirement falls further to about 20. And if you are able to save 50 percent of your take home pay, you'll begin enjoying your golden years in less than 20 years. As my mom would say, now we're cooking with gas.

The magic behind this math is the result of three related factors. First, as the saving rate increases, the amount saved increases more quickly. Second, with the passage of time, the nest egg benefits from compounding of investment returns. Finally, as the savings rate rises, the amount of money needed for living expenses goes down.

Let's get real. I know what you're thinking. The math may be accurate, but saving 30 percent or more of take home pay is impossible. Don't tell Mr. Money Mustache or the bloggers at “Early Retirement Extreme” and “Can I Retire Yet?” The fact is that early retirement is a reality for many people, including those who earned an average income during their working years.

While each early retirement story is unique, many share several common themes. Early retirees shun certain expenses many of us take for granted, such as expensive cable and cellphone packages. They tend to spend less on cars and transportation, often living close enough to work to either bike or walk. They also spend less on food, eating out less frequently than most. Finally, they are often more self-sufficient, choosing to handle home and car maintenance and repairs on their own, rather than paying others for these services.