If a $1,400 stimulus check is headed your way, investing that money in an exchange-traded fund (ETF) could pay off big time. Instead of buying a few different stocks, with an ETF you can invest in hundreds of companies. Vanguard ETFs are a smart pick because the fees are incredibly low. 

Of course, not everyone should invest their stimulus money. You should only do so if you have an emergency fund, you're current on bills, and you don't have high-interest debt. Also keep in mind that past performance doesn't guarantee future results. But if you can afford to invest and you want the potential to double your stimulus money, check out these four Vanguard ETFs. 

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1. Vanguard S&P 500 ETF (VOO)

If you invest $1,400 in the Vanguard S&P 500 ETF (VOO -0.52%) and leave it there for a long stretch, you're practically guaranteed to make money. The fund tracks the S&P 500 index, which measures the performance of 500 of the largest companies in America. Buying an S&P 500 ETF makes you an automatic investor in those 500 companies, including Apple (AAPL 0.60%), Amazon (AMZN -0.56%), Tesla (TSLA -1.57%), and Walt Disney Co. (DIS 0.25%). If you'd invested money at any point in the S&P 500's history, never once would you have lost money had you kept it invested for 20 years.

The VOO has an expense ratio of 0.03%. In other words, just 0.03% of your investment goes toward fees, which translates to $0.42 for a $1,400 investment. Had you invested $1,400 in the VOO in March 2016, you'd have just over $3,000 today. 

2. Vanguard Growth ETF (VUG)

The Vanguard Growth Fund ETF (VUG -0.60%) is a solid way to invest your stimulus check if you're OK with more risk in exchange for higher returns. It tracks an index called the CRSP U.S. Large Cap Growth Index, which is very similar to the S&P 500 screened to focus on 257 stocks identified as growth stocks. Essentially, you're investing in the faster-growing half of the S&P 500. With a 0.04% expense ratio, your fees would only eat up $0.56 of your stimulus check. 

Not surprisingly, the VUG is more heavily concentrated in the tech sector compared to S&P 500 funds. Tech stocks account for 47% of its holdings versus 27.8% for the VOO. A $1,400 investment in the VUG made five years ago would today be worth over $3,600. However, tech stocks that have soared in the past year have been cooling off recently. Temper your expectations if you're seeking huge returns immediately.

VOO Total Return Level Chart

VOO Total Return Level data by YCharts

3. Vanguard Small-Cap ETF (VB)

Investing in small-cap stocks, typically defined as those with a market capitalization between $300 million and $2 billion, is another way to earn greater returns if you're comfortable with more risk. You have the potential to invest in a future giant while it's still small, but these often young companies have a higher risk of failing.

Vanguard's Small-Cap ETF (VB -0.76%) allows you to invest in 1,426 stocks of smaller companies -- though many aren't exactly small caps, given that the median market cap is $5.9 billion. Its five largest holdings are fuel cell company Plug Power Inc. (PLUG -4.00%), solar power supplier Enphase Energy (ENPH -1.66%), cloud database MongoDB (MDB -2.89%), drug manufacturer Catalent Inc. (CTLT -0.30%), and software developer Zendesk Inc. (ZEN)

Had you invested $1,400 in the fund five years ago, you'd have more than $3,000 today. Its 0.05% expense ratio translates to fees of $0.70 on a $1,400 investment.

4. Vanguard FTSE Emerging Markets ETF (VWO)

You know how we said past performance isn't an indicator of future results? Well, had you invested $1,400 in the Vanguard FTSE Emerging Markets ETF (VWO -0.60%) five years ago, you wouldn't have doubled your money. You'd have just over $2,500 today. 

The fund invests in more than 5,000 stocks across 23 developing nations, including China, Taiwan, India, Brazil, and South Africa. Its expense ratio is 0.1%, slightly higher than the other funds on this list -- but still just $1.40 of a $1,400 investment. 

Investing in emerging markets can be risky because there's often political instability and less regulation. But consider that about 85% of the world's population lives in emerging market countries. If you're taking a long-term focus, investing in an emerging markets fund like the VWO offers serious growth potential for your third stimulus check.