It's a mistake to think that once you retire, you no longer need to invest. During retirement, investing is even more important, because it typically provides a huge part of your overall income. If you want to make sure your portfolio won't run out of cash, you need to look at investments that will provide not only consistent income but also the potential for long-term growth. The seven ETFs below fit the bill, with low expenses, diversified exposure, and risk levels that you can manage to fit with your own particular tolerance.

Exchange-Traded Fund

Expense Ratio

3-Year Average Annual Return

iShares Core S&P 500 (NYSEMKT:IVV)

0.04%

10.3%

Schwab U.S. Broad Market (NYSEMKT:SCHB)

0.03%

9.6%

Vanguard Total International Stock (NASDAQ:VXUS)

0.11%

1.4%

iShares Edge MSCI Minimum Volatility USA (NYSEMKT:USMV)

0.15%

12.1%

Schwab U.S. Dividend Equity (NYSEMKT:SCHD)

0.07%

9.3%

Vanguard High Yield Dividend (NYSEMKT:VYM)

0.08%

9%

Schwab U.S. REIT ETF (NYSEMKT:SCHH)

0.06%

2.1%

Data source: Fund companies.

Beginning with a core portfolio

Many retirement investors like to keep things simple, preferring to spend their time doing other things than watching their investments. If you're one of them, simple index-tracking funds can be the best bet. The iShares Core S&P 500 fund focuses only on the largest companies in the U.S. market as represented by the S&P 500 index. It lets retirement investors exclude smaller stocks that can be more volatile and less reliable than the tried-and-true companies in the upper ranks of the American stock market.

Schwab's U.S. Broad Market ETF takes a different approach. Rather than simply taking the top stocks, it includes the entire U.S. stock market, but with a market capitalization weighted process that still gives predominant weight to the larger companies in the market. The Schwab ETF is the pinnacle of the financial company's efforts to become the low-cost provider of the industry, sporting an expense ratio that's second to none.

Many retirement investors end up focusing solely on the U.S., but that can leave you missing a wide range of other promising alternatives. The Vanguard Total International Stock ETF includes stocks from countries around the world except for the U.S., making it a good complement to a portfolio that already has U.S. stock exposure.

ETF graph.

Image source: Getty Images.

Controlling your risk

Many retirement investors aren't entirely comfortable taking on the full risk of the stock market. Minimum volatility ETFs like the iShares fund listed above aim to tackle that risk, choosing stocks that tend to have a less dramatic response to changes in the overall market. What that generally means is that while the fund should underperform in bull markets, it should outperform in bear markets, giving investors a smoother overall ride.

The iShares fund provides a well-diversified portfolio of almost 200 stocks, with investments from the healthcare, information technology, and consumer staples sectors making up more than half of the fund's total assets. One concern that some have for minimum volatility funds in general is that they haven't shown the usual lagging performance during the current bull market, and that increases the likelihood that they might not provide the same protective element going forward. Still, the fund owns solid stocks that offer good exposure for retirement investors.

Focusing on income

Once you've taken care of your portfolio's core growth needs, the other priority that most retirement investors have is to generate enough income to cover living expenses. That's where the final few ETFs on the list can come in handy. As you can see, there are two dividend ETFs on the list, as well as another that specializes in real estate investment trusts.

Different dividend ETFs choose a variety of investing strategies. The Schwab U.S. Dividend Equity ETF focuses on high-yield stocks that have a consistent record of dividend payments. That weeds out some of the higher-yielding dividend stocks that don't necessarily have a past history of reliable dividends, and that in turn can avoid some unforeseen problems if it prevents the fund from buying stocks that subsequently reduce or eliminate their quarterly payments to shareholders.

The Vanguard High Dividend Yield ETF instead focuses first on the highest dividend yields in the market. Yet there is one concession to forward thinking, as the methodology of the underlying index uses projections of future dividend yield rather than just relying on past payouts. Both ETFs have dividend yields of about 3% right now, showing that a balanced approach to dividend stocks can be equally rewarding.

Finally, dividend stocks aren't the only way to generate income. Real estate investment trusts pay out most of their income in dividends, and their yields are often higher than those of ordinary stocks. Yet many indexes exclude REITs, meaning that if you want to own them, you have to specifically look beyond general dividend ETFs in order to get them. The Schwab REIT ETF is a solid, low-cost fund, and with a current SEC-calculated yield of 3.3%, it offers some payout advantages as well.

Be smart about investing in retirement

Stocks aren't appropriate for all of the money that retirees have squirreled away. Most retirement investors find that they're underinvested in stocks, and that makes the ETFs listed above look particularly attractive for those looking for simple investment choices after they retire.

Dan Caplinger has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.