Relying on Social Security alone won't get you a comfortable retirement. A typical benefit will replace just 40% of the average salary. Investing in dividend stocks is a smart way to supplement your income, but relying on just a few stocks is risky.

The solution: Invest in exchange-traded funds (ETFs) that offer high dividend yields so you can take advantage of diversification on top of steady income. These three Vanguard ETFs are the perfect places to start.

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Vanguard High Dividend Yield ETF (VYM)

The Vanguard High Dividend Yield ETF (VYM 0.84%) is the most popular dividend ETF in the U.S. It invests in an index of 411 stocks with the largest concentrations in the financial sector (22.4%), followed by healthcare (13.2%), and consumer staples (12.5%). 

As of March 31, the VYM had an annual yield of 2.85%. That's about double the 1.42% that the S&P 500 index has offered over the past year.

The fund tracks the FTSE High Dividend Yield Index. That index ranks U.S. stocks, not including real estate investment trusts (REITs), by projected dividend yield over a 12-month period and focuses exclusively on the higher-paying half. Because companies that can afford to pay dividends tend to be stable, the stocks the fund invests in tend to be lower risk.

A hallmark of Vanguard funds are their ultra-low fees. The VYM has an expense ratio of 0.06%, which means that just $0.60 of every $1,000 you invest will go toward fees.

Vanguard Real Estate Index Fund (VNQ)

The VYM excludes REITs, but REITs are some of the most reliable sources of dividends. That's because they're legally required to distribute at least 90% of their taxable income to shareholders.

The Vanguard Real Estate Index Fund (VNQ 0.48%) consists of about 95% equity REITs, which own and operate income-generating commercial properties. It invests the remaining sliver in real estate management and development companies. As of Feb. 28, the VNQ's 12-month yield was 3.22%.

The fund consists of 174 stocks that span the U.S. commercial real estate market. Specialized REITs, such as those that focus on cell towers, data centers, and self-storage, make up 36.8% of the portfolio, followed by residential (13.7%), industrial (10.4%), retail (10.2%), and healthcare (8.9%).

With nearly $64 billion in total assets, the VNQ is by far the largest REIT ETF in the U.S. Its expense ratio is 0.12%, significantly lower than the 0.43% average for similar ETFs. 

Vanguard International High Dividend Yield ETF (VYMI)

If you want to diversify your investment income beyond U.S. stocks, consider the Vanguard International High Dividend Yield ETF (VYMI 0.51%). It's essentially the international version of Vanguard's High Dividend Yield ETF.

The fund consists of 1,197 international stocks with the largest holdings concentrated in Japan, the United Kingdom, Taiwan, Canada, and Australia. But 28% of its holdings are in emerging markets, which tend to be riskier and have underperformed relative to U.S. stocks in the past decade. 

Its benchmark is the FTSE All-World ex U.S. High Dividend Yield Index, which takes the large- and mid-cap stocks in the FTSE All-World ex U.S. Index and ranks them according to projected dividend yield. The index invests in the half expected to produce the largest dividends in the next 12 months. Like the VYM, it excludes REITs.

The VYMI's 0.28% expense ratio is the highest of the three funds listed here. However, it's still low considering the average for similar funds is 1.12%.

The fund's 12-month yield is 3.13%, slightly higher than its U.S.-based counterpart. While the VYMI is somewhat riskier, the extra risk may be worth it for the geographic diversification and greater payout potential.