What an S&P 500 index fund is

An S&P 500 index fund is a fund that holds all 500 companies in the S&P 500 list, a collection of large U.S. companies chosen and maintained by Standard & Poor's, a financial data company. When you own shares in an S&P 500 index fund, you own a tiny piece of all 500 companies at once, rather than picking individual stocks yourself.

The fund tracks the S&P 500 index, which means its value rises and falls with the average performance of those 500 companies. If the index goes up 10 percent, the fund's value goes up roughly 10 percent (minus a small fee). If it drops 5 percent, the fund drops roughly 5 percent. You are not betting on one company or one industry — you are betting on the broad U.S. large-company market.

S&P 500 index funds exist in different forms: as mutual funds through brokerages and retirement accounts, or as exchange-traded funds (ETFs) that trade like stocks on an exchange. The mechanics are the same — you own a slice of all 500 companies — but the way you buy and sell them differs slightly.

Key Takeaways

  • An S&P 500 index fund holds shares in all 500 companies on the S&P 500 list, so your return tracks the average performance of those large U.S. companies.
  • The fund's value changes daily as the stock prices of its 500 holdings move, and you see that change reflected in your account.
  • You pay a small annual fee (called an expense ratio) to own the fund, which varies by provider and fund type but is typically between 0.03 and 0.20 percent per year.
  • S&P 500 index funds are available as mutual funds or ETFs, and you can hold them in regular taxable accounts, IRAs, 401(k)s, and other retirement accounts.

Which 500 companies are included

The S&P 500 list includes large U.S. companies across most industries: technology (Apple, Microsoft, Nvidia), finance (JPMorgan Chase, Bank of America), retail (Amazon, Walmart), healthcare (Johnson & Johnson, UnitedHealth), energy, manufacturing, and others. Standard & Poor's adds and removes companies based on size, liquidity (how easily the stock trades), and other factors, so the exact list changes over time.

The companies are weighted by market capitalization, meaning the largest companies have more influence on the fund's performance. Apple and Microsoft, for example, make up a larger portion of the fund than smaller companies on the list. This means if Apple's stock rises sharply, it pulls the whole fund's value up more than if a smaller company rises the same amount.

You do not choose which companies to include — that is Standard & Poor's job. Your role is straightforward to decide whether you want to own a piece of this particular collection of 500 large U.S. companies.

How the fund's value changes

The value of your S&P 500 index fund shares moves every trading day as the stock market opens and closes. If the 500 companies' average stock price goes up, your fund's share price goes up. If it goes down, your share price goes down. You can see this change in your brokerage account or retirement account statement.

Over longer periods — years or decades — the S&P 500 has historically trended upward, though with significant drops along the way. Past performance does not predict future results, and the fund can lose value in any given year or period. The point of holding an S&P 500 index fund is usually to own a broad, diversified slice of the large-company market rather than to chase short-term gains.

Fees and costs you pay

Every S&P 500 index fund charges an annual fee called an expense ratio, which is a percentage of the money you have invested. This fee pays for the fund company to manage the fund, keep the list updated, and handle trades. The expense ratio is deducted automatically from the fund's returns, so you do not write a check — it straightforward reduces what you earn.

Expense ratios for S&P 500 index funds vary by provider. Some of the largest fund companies (Vanguard, Fidelity, Schwab) offer S&P 500 index funds with expense ratios as low as 0.03 to 0.04 percent per year. Other providers charge 0.10 to 0.20 percent or higher. Over decades, even a small difference in fees compounds, so comparing expense ratios matters if you are choosing between funds.

You may also pay a transaction fee when you buy or sell shares, depending on your brokerage. Many brokerages now offer commission-free trading on index funds, but some still charge. Check your brokerage's fee schedule before you invest.

S&P 500 index funds versus picking individual stocks

An S&P 500 index fund spreads your money across 500 companies, so if one company performs poorly, it has a small effect on your overall return. If you pick individual stocks, one bad choice can hurt your portfolio significantly. Index funds reduce this risk through automatic diversification.

Index funds also require far less time and research than picking stocks. You do not need to read earnings reports, follow company news, or decide when to buy and sell. The fund straightforward holds all 500 companies and rebalances as the list changes.

The trade-off is that you cannot outperform the S&P 500 with an index fund — you will match its performance (minus fees). If you believe you can pick stocks that will beat the market, an index fund is not the right choice. Most individual investors, however, do not consistently beat the market over long periods, which is why index funds appeal to many people.

Where you can hold an S&P 500 index fund

You can own S&P 500 index funds in a regular taxable brokerage account, where you pay taxes on any gains or dividends each year. You can also hold them in tax-advantaged retirement accounts: a traditional IRA, Roth IRA, SEP IRA, Solo 401(k), or an employer-sponsored 401(k) or 403(b). The tax treatment differs depending on the account type, but the fund itself works the same way.

Most major brokerages (Fidelity, Schwab, E-Trade, Vanguard, Interactive Brokers) and many banks offer S&P 500 index funds. If you have a 401(k) through your employer, your plan likely includes at least one S&P 500 index fund option. Check your plan documents or contact your plan administrator to see what is available.

Dividends and reinvestment

Many of the 500 companies in the S&P 500 pay dividends — cash payments to shareholders, usually quarterly. When a company in the fund pays a dividend, the fund collects it and passes it to you. You can choose to receive the dividend as cash or have it automatically reinvested to buy more shares of the fund.

Reinvestment is often the default in retirement accounts and is usually the simpler choice, because it compounds your returns over time without requiring you to make a decision. In a taxable account, dividends are taxable income in the year you receive them, whether you reinvest or take the cash.

Frequently Asked Questions

Can I lose all my money in an S&P 500 index fund?

Theoretically, yes, if all 500 companies went to zero value. In practice, this is extremely unlikely. The S&P 500 includes the largest, most established U.S. companies, and the index has recovered from every major crash in its history. You can lose a significant portion of your money in a severe market downturn, but total loss is not a realistic risk.

How often does the S&P 500 list change?

Standard & Poor's adds and removes companies throughout the year as market conditions change. Changes are typically announced in advance, and the fund automatically adjusts its holdings. You do not need to do anything — the fund manager handles the rebalancing.

What is the difference between an S&P 500 mutual fund and an S&P 500 ETF?

Both hold the same 500 companies and track the same index. The main differences are how you buy them (mutual funds through a brokerage account, ETFs like stocks on an exchange), when you can trade them (mutual funds once per day after market close, ETFs during market hours), and sometimes the expense ratio. For long-term investors, the differences are minor.

Do I need to rebalance an S&P 500 index fund myself?

No. The fund manager rebalances automatically as companies are added or removed from the S&P 500 list and as stock prices change. You straightforward hold the fund and let it do its job.

Is an S&P 500 index fund the same as a total stock market index fund?

No. An S&P 500 index fund holds only the 500 largest U.S. companies. A total stock market index fund holds thousands of U.S. companies of all sizes, including mid-size and small companies. Total market funds are more diversified but often have similar long-term returns.