Becoming a millionaire sounds daunting. Indeed, it's not easy, but you can achieve your goal, particularly if you start early. That way, you can benefit from compounding over a longer period. A long period also smooths out that pesky short-term volatility. Based on achieving a certain annualized return, you can also figure out how much you need to invest each month.

One way to achieve your goal is to invest in exchange-traded funds (ETFs). These allow you to diversify your portfolio, but the ETFs trade like stocks. If you want to invest in an index, Vanguard offers a wealth of low-cost options.

Narrowing your choices down to three can seem overwhelming, but these ETFs could help you reach millionaire status.

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1. Vanguard Russell 3000 ETF

The Vanguard Russell 3000 Index Fund ETF (NASDAQ:VTHR) is a way to invest in nearly the entire U.S. stock market. The more than 3,000 holdings represent 98% of the domestic market.

U.S. equities have done well for a long time. Over the last year, the fund returned nearly 32%. In the last decade, you would have received almost 15% per year. During that time, your money would've grown by nearly fivefold.

Of course, the past is no guarantee for the future. However, it's fairly safe to assume that the U.S. stock market will perform well over the long haul.

2. Vanguard FTSE All-World ex-U.S. ETF

Now that you've gotten the U.S. stock market covered, you might want to add geographic diversification by investing in the rest of the world. The Vanguard FTSE All-World ex-U.S. ETF (NYSEMKT:VEU) is a good way to go.

The fund invests in about 3,600 stocks across the globe. It puts most of its assets, 40%, in Europe, with another 27% in the Pacific and 25% in emerging markets. Most of the remaining funds, 6%, are invested in North America.

Hence, you get a wide range of stocks spread out over the entire world. That's beneficial in case one region runs into problems.

This ETF returned nearly 24% over the past year and has an average annual return of about 8% over the last 10 years. During that span, you would've more than doubled your money.

3. Vanguard Long-Term Corporate Bond Index ETF

It's not a bad idea to add bonds to your portfolio to add more stability and a steady income generator. There's a variety from which to choose, but the Vanguard Long-Term Corporate Bond Index ETF (NASDAQ:VCLT) has some nice characteristics.

The fund invests mostly in investment-grade corporate bonds, which tend to hold up better than lower-rated bonds since the credit quality is better. About 51% of the assets were in BBB-rated bonds, and another 38% were rated A.

Of course, you could invest in U.S. government securities, but investment-grade bonds have a higher yield, 3.1%, for the extra risk. The fund also buys securities with longer maturities. Vanguard gives it a risk rating of 3, right in the middle of its five-point scale.

Over the last year, the return was only 2.5%. But its 10-year annualized return was 6.8%, meaning you would have roughly doubled your money in that span.

While the two equity funds are at the higher end of the risk spectrum, the bond fund moderates this somewhat. Additionally, if you have a long time horizon, you should get rewarded for this elevated risk.

The nice part is, since these are index funds, Vanguard keeps expenses ultra low. These range from 0.05% to 0.10%. Of course, since the funds spend less money on certain administrative functions, that means you get a higher return.

While going after high-return funds is exciting, these steady, low-cost options are one way to help you reach millionaire status.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.