Sock away $20 a day, every day, and it's very likely that you'll retire a millionaire.

Not by stuffing it under your mattress, though. Twenty bucks a day under your mattress would give you a million bucks ... after more than 135 years.

That's twice the normal retirement age!
If you want a reasonable chance of amassing that kind of wealth in a normal career -- not to mention a normal lifetime -- you must invest. And how you invest may make all the difference.

Ten-year Treasury notes recently offered a 3.49% yield. Investing your daily $20 in those bonds instead of your mattress would get you to millionaire status in around 50 years. We're getting closer.

Agree to take on a bit more volatility, though, and you can position yourself to do better than that. Over the long haul, the stock market has historically returned an average of about 10% to 11% annually. For the sake of example, let's say that pace keeps up. In that case, investing in a low-cost market index tracker such as the iShares S&P 500 (AMEX: IVV) exchange-traded fund will get you to $1 million in roughly 26 years.

Things get more interesting when you invest with a strategy that has a legitimate chance to beat the market. If, over the long haul, you outpaced Wall Street's averages by a mere 2 percentage points a year, $1 million would be yours in just a bit more than 23 years.

That's a big "if"
Of course, very few investors have reliably outperformed the market over time spans measured in decades. Those who have -- Warren Buffett, John Neff, Walter Schloss, Peter Lynch, and Charles Munger, to name a few -- often reach legendary status.     

Although you and I may never achieve the tremendous level of returns that these masters have earned, their stories show that the market can be, and has been, beaten.

Don't worry, get rich
Regardless of whether you'd like to try to trounce Wall Street or just keep pace with the market, the takeaway is still the same: To amass a comfortable nest egg in a reasonable time frame, you must own stocks or stock funds.

If you go the individual stock route, there is some good news. You don't need to be invested in unfamiliar places to make money over the long haul. With many well-known and well-loved companies trading at decent prices, you can buy the names you know and do just fine. Perhaps you've heard of:




Apple (Nasdaq: AAPL)



Harley-Davidson (NYSE: HOG)



Wrigley (NYSE: WWY)



Caterpillar (NYSE: CAT)



Tiffany (NYSE: TIF)



Starbucks (Nasdaq: SBUX)



Brand-rank data from BusinessWeek. Returns as of Feb. 29, 2008.

Each of those companies is a powerhouse with decent long-term prospects. None is likely to double overnight. Then again, they're not exactly at a high risk of falling off the face of the earth in the next week, either. And as you can see, they've all made money for their investors. By turning in at least a 7.2% annualized return, they've helped people more than double their stakes in a decade. Not too shabby for some of the biggest names around.

Get started now
Of course, there's a catch. If you really want a shot at becoming a millionaire on $20 a day, you have to be committed to the plan for the long haul. The toughest part might be finding the discipline to slog along, day after day, for a goal that's a few decades away.

That's where my colleague Robert Brokamp at Motley Fool Rule Your Retirement can help. By regularly showcasing great tools, techniques, and tips to keep you on track, and by connecting you with other like-minded prospective retirees, he can help you keep the focus you need to succeed. You can take 30 days to tour the service, absolutely free.

This article was originally published Nov. 3, 2006. It has been updated.

At the time of this publication, Fool contributor Chuck Saletta did not own shares of any company mentioned in this article, but his wife owned shares of Harley-Davidson. Apple and Starbucks are Motley Fool Stock Advisor recommendations, and Starbucks is also recommended in Inside Value. Wrigley is an Income Investor selection. The Fool has a disclosure policy.