If your second stimulus check hasn't arrived yet, expect it to appear in your bank account any day. For millions of Americans, that check will be a lifeline to help with bills, boost emergency savings, or pay down credit card debt. But if you aren't struggling financially, one of the best ways to put that money to work is to invest it.

But $600 will only go so far, and you may be hesitant to use it all to buy a couple of shares of an individual stock. A good alternative: Invest your money in a high-growth index fund. One option for investors with an appetite for risk is the Invesco QQQ Trust (QQQ 0.14%).

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How to turn a $600 stimulus check into $3,768

Had you invested $600 in the Invesco QQQ Trust on Jan. 3, 2011, you'd have almost $4,000 today -- or, to be precise, $3,768.60 as of Jan. 4, 2021. In the past 10 years, the fund has delivered returns of 528.1%. Just in the last year, it's grown investors' money by 47.5%. 

Invesco QQQ Trust is an exchange-traded fund, or ETF. Instead of investing your money in a single company, buying shares invests your money in the 100 largest non-financial stocks listed on the Nasdaq stock market. If the stocks in the index go up or down, your investment's value increases or decreases by about the same amount. But because the index is dominated by fast-growing tech stocks, the Invesco ETF has mostly gone up in the past 10 years.

For instance, the fund's 10 largest holdings now are Apple, Microsoft, Amazon, Tesla, Facebook Class A shares, Google parent company Alphabet Class C and Class A shares, NVIDIA, PayPal, and Adobe

The fund has a pretty low expense ratio of 0.2%. That means if you invested $600, only $1.20 would be gobbled up by investment fees each year.

QQQ Total Return Level Chart

QQQ Total Return Level data by YCharts

Could I lose money by investing in Invesco QQQ Trust?

Over the past decade, the Invesco QQQ Trust has smashed the returns of the S&P 500 index, which tracks the stocks issued by 500 of the largest corporations in the U.S. But that certainly doesn't mean it will deliver those kinds of returns in the next 10 years. Past performance should never be confused as a guarantee of future results.

Whenever you invest, there's a risk that you'll lose money. You can improve your odds of success by only investing money in stocks when you don't need it in the next five to 10 years, so your investment has plenty of time to recover if the market plummets.

One thing to know is that the high returns the ETF has delivered also come with high risk, because the fund isn't exactly a diversified investment. Sure, it's more diversified than investing in a handful of companies, but nearly half of its holdings are in the technology sector. A truly diversified portfolio isn't so heavily concentrated in a single sector.

Therefore, the Invesco QQQ Trust can be a good vehicle for delivering astounding returns, but you should only consider investing in it if you're already invested across the broader stock market. Given that it's a high-risk investment, be extra cautious about buying shares if you're close to retirement.

How to buy shares of the Invesco QQQ Trust

ETFs like the Invesco QQQ Trust are bought and sold exactly like regular stocks via stock exchanges. If you want to purchase shares, you'll need a brokerage account. As of Jan. 4, the ETF was trading at just over $309. So to invest exactly $600, you'd need to use a brokerage that allows you to buy fractional shares of ETFs. Otherwise, you'd have to cough up an extra $18 and change to buy a second share.

Just remember that financial security is a lot more valuable than big returns. So if having an extra $600 in your bank account would help you sleep better at night, that's exactly where your second stimulus check belongs.