It's no surprise that exchange-traded funds (ETFs) have become so popular over the past decade. They offer investors the ability to invest in wide swaths of the market in one portfolio that can be traded like an individual stock. For the investor who doesn't have the time, resources, or inclination to hire a broker or build a broadly diversified portfolio of stocks, they are a terrific option.

The S&P 500 is made up of the 500 largest companies in the U.S., which represents about 80% of the available market cap, and is considered the best gauge of the performance of large-cap U.S. stocks. As such, there is more than $5 trillion in indexed assets invested in the S&P 500, including more than a dozen ETFs.

Through just one of these ETFs, you get access to the 500 largest companies in the U.S. without buying shares of them individually. It begs the question: Could you retire a millionaire by investing in just the S&P 500 alone? Let's take a look.

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The S&P 500 has returned about 10% per year over time

The origins of the S&P 500 date back to 1926, but that early incarnation only tracked the 90 largest stocks. The S&P 500 came into existence on March 4, 1957. Since then, it has posted an average annual return of about 8.2%. When you include reinvested dividends, it's about 10.5%. When you think about all that has happened over the last 64 years or so, that's a pretty good return that most of us would be happy to get on our investments.

This past decade has been a particularly good one for the S&P 500, as it has posted an annualized return of about 14.5% over the past 10 years through Nov. 18.

While it is impossible to know what the next 10, 20, or 40 years will bring, for the purposes of this hypothetical, let's say the index averages a 10.5% annualized return over the next 25 years, which is in line with historical averages. It is also the approximate annualized return of the SPDR S&P 500 Trust (SPY 1.19%), which is not only the first ETF, introduced in 1993, but the largest, with about $435 billion in assets. Since inception, the SPDR S&P 500 Trust ETF has posted an annualized return of roughly 10.6%. Could that investment alone make you a millionaire?

Will it make you a millionaire?

To answer the question posed above, it takes a long time investing in the S&P 500 alone through an ETF to make you a millionaire. One scenario would involve investing about $300 per month, for 30 years, with a $10,000 initial investment, to even get close to $1 million. If that sounds doable -- then that's great. 

A more realistic scenario for many investors could be to start with an investment of, say, $5,000 and invest $150 per month in an S&P 500-based ETF. If you are in your 40s and did that for 25 years, you would have about $285,000. With $100 per month, it would be about $212,000.

If you are in your 30s and have a longer time horizon, say, 30 years, you'd have close to $500,000 for retirement investing $150 per month.

But if you have it as a core holding in your portfolio, in addition to Social Security and any other investments you have accumulated through your employer, or elsewhere, you certainly could exceed that $1 million plateau.

To get a better sense of where you are, where you need to go, and how to get there, consult a financial advisor. They have tools that can project how much you'll need in retirement based on your expected lifestyle and expenses and recommend a plan to get you there.