Start with what you're saving for and how long you have

The index fund that makes sense for you depends on two things: when you'll need the money and how much risk you can handle while waiting. If you're saving for retirement and won't touch the money for 30 years, you can own funds that go up and down a lot. If you're saving for a house down payment in five years, you want something steadier. Your time horizon — not the fund's name or how popular it is — should drive your choice.

Start by naming the goal and the year you'll need the money. Write it down. This single piece of information eliminates most of the confusion people feel when looking at fund lists. A 25-year-old saving for retirement at 65 is in a completely different situation than a 55-year-old doing the same thing, even though they're both saving for retirement.

Key Takeaways

  • A total stock market index fund (tracking the S&P 500 or broader U.S. market) is the most common choice for long-term retirement savings because it owns hundreds of companies and spreads risk.
  • A target-date fund automatically shifts from stocks to bonds as you approach retirement, so you don't have to rebalance it yourself.
  • International index funds add exposure to companies outside the U.S., but most financial advisors suggest keeping them to 20 to 30 percent of your stock holdings.
  • Bond index funds are steadier than stock funds but grow more slowly, and they make more sense the closer you get to needing the money.
  • The fund's expense ratio — what it costs to own it each year — matters more than trying to pick the "best" fund, because lower costs compound into real money over decades.

U.S. stock index funds for long-term growth

If you're saving for retirement and have at least 10 years before you need the money, a total U.S. stock market index fund is the standard choice. These funds track either the S&P 500 (the 500 largest U.S. companies) or a broader index that includes mid-size and smaller companies too. Both are legitimate choices; the difference is small enough that it shouldn't be your deciding factor.

Common examples include funds tracking the S&P 500, the Wilshire 5000 (which includes more companies), or the Russell 3000. Your brokerage will offer versions of these from different fund companies — Vanguard, Fidelity, and Schwab all offer low-cost versions. The fund name will usually include the word "index" and the index it tracks. A fund called "Vanguard Total Stock Market Index Fund" does exactly what the name says: it buys a small piece of hundreds of U.S. companies to match the total market.

These funds work because they own so many companies that no single one can sink your investment. When one company struggles, hundreds of others keep growing. Over long periods — 20 years or more — U.S. stock market index funds have historically grown faster than bonds or savings accounts, which is why they're the backbone of most retirement plans.

Target-date funds if you want one fund to do the work

A target-date fund is an index fund that automatically changes what it owns as you get older. You pick the fund with the year closest to when you'll retire — for example, "Target Date 2050" if you plan to retire around 2050. When you buy it, the fund owns mostly stocks because you have time to ride out market swings. As 2050 approaches, the fund gradually sells stocks and buys bonds instead, becoming steadier and safer.

This matters because most people should own more stocks when young and more bonds when old, but most people don't rebalance on their own. A target-date fund does it automatically. You buy it once and don't have to think about it. Vanguard, Fidelity, and Schwab all offer target-date index funds with low costs.

The trade-off is that you give up control over the exact mix. The fund company decides how much to shift each year, and you follow their schedule. For most people, this is fine — the fund company's schedule is reasonable. But if you want to own 80 percent stocks at age 50 instead of the 60 percent the fund owns, a target-date fund won't let you do that without switching to separate funds.

International index funds for exposure outside the U.S.

An international index fund owns companies in other countries — Europe, Japan, Australia, and emerging markets. Many financial advisors suggest owning some international exposure because the U.S. is not the whole world economy, and international stocks sometimes grow when U.S. stocks don't.

The question is how much. A common approach is to own 70 to 80 percent U.S. stock index funds and 20 to 30 percent international index funds. Some people own none. There's no single right answer, but most long-term investors own at least some international exposure. Common international index funds track the MSCI EAFE (developed countries outside the U.S.) or the MSCI Emerging Markets (faster-growing countries like India and Brazil).

International funds add complexity because they're affected by currency changes — if the dollar gets stronger, international stocks become less valuable in dollar terms, even if the companies themselves are doing well. This is one reason to keep international holdings smaller than U.S. holdings: the extra moving parts mean extra risk.

Bond index funds when you're getting closer to needing the money

A bond index fund owns thousands of bonds — loans to governments and companies. Bonds don't grow as fast as stocks, but they don't swing up and down as much either. When stock markets fall hard, bond prices often stay steady or even rise, which is why bonds are useful for balance.

Most people should own mostly stocks in their 20s and 30s, shift toward a mix of stocks and bonds in their 40s and 50s, and own more bonds than stocks once they're within 10 years of retirement. A common rule of thumb is to own your age in bonds — if you're 40, own 40 percent bonds and 60 percent stocks. This is not a law, just a starting point.

Common bond index funds track the Bloomberg U.S. Aggregate Bond Index (a mix of government and corporate bonds) or the U.S. Treasury Index (only government bonds). Treasury bonds are safer but pay less. Aggregate bond funds pay a bit more but own some corporate bonds, which carry slightly more risk. For most people, an aggregate bond index fund is the right choice.

How to compare funds: focus on expense ratios, not performance

When you look at a list of index funds, you'll see performance numbers — how much the fund returned last year or over the past five years. Ignore these. Index funds tracking the same index should have nearly identical performance because they own nearly the same things. The difference between them comes down to cost.

The expense ratio is the percentage of your money the fund company charges each year to run the fund. A fund with a 0.03 percent expense ratio costs $3 per year for every $10,000 you own. A fund with a 0.50 percent expense ratio costs $50 per year for the same $10,000. Over 30 years, that difference compounds into thousands of dollars in extra money you keep instead of paying the fund company.

Look for index funds with expense ratios under 0.20 percent. Vanguard, Fidelity, and Schwab all offer index funds with ratios between 0.03 and 0.10 percent. If a fund charges more than 0.50 percent, it's probably not an index fund — it's an actively managed fund, which is a different product entirely. Stick with the low-cost index funds.

A straightforward starting portfolio for most people

If you're overwhelmed by choices, here's a portfolio that works for most people saving for retirement: own a total U.S. stock market index fund and a bond index fund in a mix that matches your age (your age in bonds, the rest in stocks). If you want international exposure, move 20 percent of your stock money into an international index fund. That's it. You don't need 10 funds or a complicated strategy.

If you want even simpler, buy a target-date fund with the year closest to your retirement. One fund, automatic rebalancing, done. The performance won't be dramatically different from a hand-built portfolio, and you'll spend less time worrying about it.

Frequently Asked Questions

Should I pick an index fund based on past performance?

No. Index funds tracking the same index have nearly identical performance because they own the same companies. The fund that performed best last year might perform worst next year. Instead, compare expense ratios — the annual cost to own the fund. Lower costs are the only reliable advantage one index fund has over another.

Is the S&P 500 enough, or do I need other funds too?

The S&P 500 is a solid core holding for long-term investors. Many people own only an S&P 500 index fund and a bond index fund and do fine. Adding international exposure and smaller U.S. companies is reasonable but optional. The S&P 500 alone is not a mistake.

What's the difference between a fund and an ETF?

Both are baskets of investments. Index funds are mutual funds you buy directly from the fund company or through a brokerage. ETFs (exchange-traded funds) trade like stocks on an exchange. For index investing, the difference is small — both can be low-cost, and both track the same indexes. Pick whichever your brokerage makes easiest to buy.

Can I own index funds in a regular brokerage account, or do I need a retirement account?

You can own index funds in either. A regular brokerage account has no contribution limits but you pay taxes on gains each year. A retirement account like a 401(k) or IRA lets you defer taxes until you withdraw the money. Most people should max out retirement accounts first, then use a regular account for additional savings.

How often should I rebalance my portfolio?

Once a year is standard. If you own 60 percent stocks and 40 percent bonds, and stocks grow so much that you now own 70 percent stocks, you can sell some stocks and buy bonds to get back to 60/40. This forces you to sell high and buy low, which is good discipline. But rebalancing once a year is enough — rebalancing every month is overkill and wastes money on trading costs.