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

The index fund that makes sense for you depends almost entirely on two things: when you'll need the money and how comfortable you are with your balance going up and down in the short term. A fund tracking the S&P 500 will swing more month to month than a bond index fund, but historically grows faster over decades. A fund that holds both stocks and bonds sits in the middle. Before you pick a fund, write down when you plan to use this money — retirement at 65, a house down payment in five years, or something else.

Once you know your timeline, you can narrow down the type of index fund. Someone investing for 30 years can weather big swings and might choose a stock-heavy fund. Someone saving for a goal three years away should look at bond funds or balanced funds that mix stocks and bonds. This isn't about picking the "best" fund — it's about picking one that won't force you to sell at the wrong time because you panicked.

Key Takeaways

  • Stock index funds (like those tracking the S&P 500) historically grow faster over long periods but drop sharply in bad years, so they work best if you won't need the money for at least five years.
  • Bond index funds are less volatile and provide steadier returns, making them suitable for money you'll need within a few years or for investors who lose sleep over market swings.
  • Total market funds track thousands of companies instead of 500, spreading risk across more holdings, and are a straightforward choice for beginners who want broad exposure.
  • Your brokerage (Fidelity, Vanguard, Charles Schwab, or others) offers its own index funds alongside funds from other companies, so compare expense ratios before you decide.
  • The expense ratio — what the fund charges yearly as a percentage of your money — matters more than picking the "right" index because even small differences compound over decades.

Stock index funds for long-term growth

A stock index fund tracks a group of company shares. The most common is an S&P 500 fund, which holds shares in 500 large U.S. companies. When you own a share of an S&P 500 index fund, you own a tiny piece of all 500 companies at once. Other stock index funds track the entire U.S. market (including smaller companies), international stocks, or specific sectors like technology or healthcare.

Stock index funds are the right choice if you're investing money you won't touch for at least five to ten years. They grow faster than bonds over long periods, but they also drop 20, 30, or even 40 percent in bad years. If you'd panic and sell during a crash, a stock fund will hurt. If you can ignore the swings and keep investing, stock funds have historically been the better choice for building wealth over decades.

The S&P 500 is the most popular starting point because it's straightforward, well-known, and includes companies most people recognize. But a total U.S. stock market fund is also a solid choice — it holds the S&P 500 companies plus thousands of smaller ones, so you're even more diversified. Both are offered by nearly every brokerage under slightly different names (Vanguard calls theirs VTSAX, Fidelity calls theirs FSKAX, and so on).

Bond index funds for stability and income

A bond index fund holds IOUs from governments or companies. When you own a bond fund, you're lending money to these borrowers, and they pay you interest. Bond funds don't grow as fast as stock funds over long periods, but they're much steadier — they rarely drop more than 5 or 10 percent even in rough years, and they pay you regular income.

Bond index funds make sense if you need the money within three to five years, if you're uncomfortable with big swings, or if you're nearing retirement and want to protect what you've already saved. The most common choice is a total bond market fund, which holds thousands of government and corporate bonds of different lengths and types. These funds are less exciting than stock funds, but that's the point — they're supposed to be boring and reliable.

Be aware that bond funds do drop when interest rates rise, because existing bonds become less attractive. But this drop is usually small and temporary. If you hold the fund until maturity (or close to it), you'll get your money back plus the interest you earned along the way.

Balanced and target-date funds for hands-off investing

A balanced fund mixes stocks and bonds in a fixed ratio — often 60 percent stocks and 40 percent bonds, or 70/30. This approach reduces the swings you'd see in an all-stock fund while still giving you growth. A target-date fund goes further: it automatically shifts from stocks toward bonds as you get closer to your target retirement year. A 2050 target-date fund starts stock-heavy and gradually becomes more conservative, so you don't have to rebalance it yourself.

These funds are useful if you want to set it and forget it, or if you're not sure how much risk you can handle. The trade-off is that you're paying for someone else to do the rebalancing, which costs a bit more in fees. But for many people, the simplicity is worth it — you pick one fund based on your retirement year and stop thinking about it.

Compare expense ratios, not just fund names

Two S&P 500 index funds from different companies will track the same 500 stocks, but they charge different fees. The expense ratio is the yearly cost, shown as a percentage. A fund charging 0.03 percent costs $3 per year on a $10,000 investment. A fund charging 0.50 percent costs $50 on the same amount. Over 30 years, that difference compounds into thousands of dollars.

Most index funds from major brokerages (Vanguard, Fidelity, Charles Schwab, Schwab) charge between 0.03 and 0.20 percent. Avoid funds charging more than 0.50 percent — those are usually actively managed funds that try to beat the market, not index funds. You can find the expense ratio on the fund's fact sheet or on your brokerage's website before you buy.

Don't assume your brokerage's own funds are cheaper or better. Vanguard's S&P 500 fund might have a lower expense ratio than Fidelity's, or vice versa. Spend five minutes comparing the funds available to you and pick the one with the lowest fee for the index you want to track.

Understand what index you're actually buying

The name of a fund doesn't always tell you exactly what it holds. "Large-cap" funds hold big companies. "Mid-cap" and "small-cap" hold medium and small companies. "Total market" holds all three. "International" or "developed markets" holds companies outside the U.S. "Emerging markets" holds companies in faster-growing countries with more risk.

Before you buy, read the fund's fact sheet or prospectus — a one-page summary that lists the index it tracks, the top ten holdings, and the expense ratio. This takes five minutes and prevents surprises. If you're not sure what a fund holds, your brokerage's website has a search tool that shows you the details.

A common beginner strategy is to buy one total U.S. stock market fund and one international stock fund, or one total U.S. stock market fund and one bond fund. This gives you diversification without overthinking it. You don't need to own 20 different index funds — most people do better with three to five.

Where to buy index funds

You buy index funds through a brokerage — a company that holds your money and lets you trade. The major ones are Vanguard, Fidelity, Charles Schwab, and E*TRADE. Each offers its own index funds and also sells index funds from other companies. You open an account, deposit money, and buy the fund you want. The process takes about 15 minutes online.

Most brokerages don't charge a commission to buy or sell index funds anymore, so the only cost is the fund's expense ratio. Some brokerages offer slightly better rates on their own funds, but the difference is usually small. Pick a brokerage you trust and that has a website or app you find straightforward to use — you'll be logging in to check your balance, and you want that to be straightforward.

Frequently Asked Questions

Should I buy an S&P 500 fund or a total market fund?

Both are solid choices for long-term investors. The S&P 500 is simpler and more well-known. A total market fund includes smaller companies too, so it's slightly more diversified. The difference in returns over 20 years is usually small. Pick whichever has the lower expense ratio at your brokerage.

Can I mix different index funds in one account?

Yes. Many investors hold a U.S. stock fund, an international stock fund, and a bond fund in the same account. This is called diversification. You can set up automatic monthly deposits that split between the funds, or buy them all at once. Your brokerage lets you hold as many funds as you want.

What if the market crashes after I buy?

If you're investing for 10+ years, market crashes are normal and temporary. Historically, the market has recovered and gone higher every time. The worst thing you can do is sell during a crash. If you're investing money you'll need in a few years, use a bond fund instead — it won't drop as much.

Do I need to pick individual stocks instead of index funds?

No. Index funds are simpler, cheaper, and historically outperform most people who pick individual stocks. Unless you enjoy researching companies and have time to do it, an index fund is the better choice. Most professional investors recommend index funds for beginners and experienced investors alike.

How often should I check my index fund balance?

Once or twice a year is enough. Checking too often tempts you to panic-sell during dips or chase performance. Index funds are meant to be boring — you buy them, hold them, and let time do the work. Set a reminder to review your account once a year and rebalance if needed, then move on.