Key Points

  • Over the past 100 years, the S&P 500 has generated an average annual return of around 10%.

  • With those kinds of returns, even small investments can grow substantially over years.

  • Here's exactly how much $100 a month could turn into over the next two decades.

  • 10 stocks we like better than Vanguard S&P 500 ETF ›

A lot of people think it takes a lot of money to make money investing in the stock market. In reality, any investment can do the job. Even small monthly investments made consistently over the course of decades.

For many people, a simple $100 monthly investment in the S&P 500 (SNPINDEX: ^GSPC) is achievable. It may not sound like much, but how large can your investment grow if you keep investing for 20 years?

Missed Nvidia in 2009? This Rare Signal Is Flashing Again. In 2009, a "Double Down" signal flashed for a little-known chipmaker called Nvidia. For the first time in years, that same "Total Conviction" signal is flashing for a company 1/100th the size of Nvidia. Continue »

What $100 a month in the S&P 500 turns into

Historically, the S&P 500 has generated an average annual return of around 10% over the past century. While returns can fluctuate significantly in the short term, a 10% annual rate of return assumption gives us a good benchmark to work with.

Assuming an investor starts with nothing and consistently contributes $100 a month to something like the Vanguard S&P 500 ETF (NYSEMKT: VOO), at a 10% average annual return, those investments would turn into roughly $76,000.

That means your total of $24,000 in contributions would have generated roughly $52,000 in investment gains. Once the snowball effect of those monthly investments accelerates, the majority of your returns come from compounding, not from the investments themselves.

Consistency matters more than anything

Most people assume that the rate of return you see on your investments is the most important factor in how big your portfolio can become. There's no question it's a major catalyst, but it's not the biggest one.

The ability to consistently contribute to your investment account is perhaps the most important thing for long-term wealth creation.

There will be times when the market declines, occasionally very significantly. But it's the ability to continue investing through those times that could create the biggest benefit. That's because in those situations, you're buying shares at a discount. Taking advantage of those periods could actually improve your long-term returns over pausing your investments when the market gets rougher.

Should you buy stock in Vanguard S&P 500 ETF right now?

Before you buy stock in Vanguard S&P 500 ETF, consider this:

The Motley Fool Stock Advisor analyst team just identified what they believe are the 10 best stocks for investors to buy now… and Vanguard S&P 500 ETF wasn’t one of them. The 10 stocks that made the cut could produce monster returns in the coming years.

Consider when Netflix made this list on December 17, 2004... if you invested $1,000 at the time of our recommendation, you’d have $430,571!* Or when Nvidia made this list on April 15, 2005... if you invested $1,000 at the time of our recommendation, you’d have $1,399,268!*

Now, it’s worth noting Stock Advisor’s total average return is 986% — a market-crushing outperformance compared to 214% for the S&P 500. Don't miss the latest top 10 list, available with Stock Advisor, and join an investing community built by individual investors for individual investors.

*Stock Advisor returns as of August 29, 2026.

David Dierking has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.