An S&P index fund tracks the 500 largest U.S. companies by market value

An S&P index fund is a mutual fund or exchange-traded fund (ETF) that holds the same stocks as the Standard & Poor's 500 Index. The S&P 500 is a list of 500 large U.S. companies ranked by their total market value — companies like Apple, Microsoft, Coca-Cola, and JPMorgan Chase. When you own shares in an S&P index fund, you own a small piece of all 500 companies at once.

The fund manager does not pick which stocks to buy or sell based on research or prediction. Instead, the fund straightforward holds the stocks that belong in the S&P 500 at the same weights they have in the index. If Apple makes up 7% of the index, your fund holds 7% Apple. This is called passive management, and it is the defining feature of an index fund.

The S&P 500 is maintained by S&P Dow Jones Indices, a division of S&P Global. That company decides which companies meet the size and liquidity requirements to be included. When a company grows large enough or shrinks too small, S&P Dow Jones adds or removes it from the list, and the index funds holding that index adjust their holdings to match.

Key Takeaways

  • An S&P index fund holds all 500 stocks in the S&P 500 Index in the same proportions, so you own a piece of 500 large U.S. companies with one investment.
  • The fund does not try to beat the market — it straightforward mirrors the index, which is why costs are typically lower than actively managed funds.
  • You can buy S&P index funds as mutual funds (which trade once per day) or as ETFs (which trade throughout the day like stocks).
  • The fund's value rises and falls with the overall value of the 500 companies it holds, so you experience the same gains and losses as the index itself.

How the fund's value changes

The value of your S&P index fund shares moves with the value of the 500 companies inside it. If those companies' stock prices rise on average, your fund's price rises. If they fall, your fund's price falls. You do not own the index itself — you own shares of a fund that holds the stocks, so the price per share reflects what those stocks are worth on any given day.

The S&P 500 is often used as a measure of how the overall U.S. stock market is performing, because these 500 companies represent about 80% of the total value of all U.S. publicly traded stocks. When financial news reports say "the market was up 2% today," they are often referring to the S&P 500 or a similar broad index.

Mutual funds versus ETFs that track the S&P 500

You can own an S&P index fund in two forms: as a mutual fund or as an exchange-traded fund (ETF). Both hold the same stocks and track the same index, but they work differently in practice.

A mutual fund version of an S&P index fund trades once per day, after the stock market closes. You place an order during the day, but the price you pay is set at the end of the trading day. You cannot see the exact price until after the market closes. Mutual funds are bought directly from the fund company or through a brokerage account.

An ETF version trades throughout the day like a stock. You can buy or sell shares at any time while the market is open, and you see the price in real time. ETFs often have lower expense ratios (the annual cost to own them) than mutual fund versions of the same index. Both types are offered by major fund companies like Vanguard, Fidelity, and Schwab.

Expense ratios and what you pay to own the fund

An expense ratio is the annual percentage cost of owning the fund. Because an S&P index fund straightforward mirrors the index rather than paying managers to research stocks, the expense ratio is typically very low — often between 0.03% and 0.20% per year. This means if you own $10,000 in the fund, you pay between $3 and $20 per year in fees.

Different fund companies charge different amounts for their S&P 500 index funds. Vanguard's S&P 500 ETF (ticker: VOO) has an expense ratio of 0.03%. Fidelity's S&P 500 Index Fund (ticker: FXAIX) charges 0.015%. Schwab's U.S. Large-Cap ETF (ticker: SCHX) charges 0.03%. These differences are small in dollar terms but compound over decades of ownership.

Beyond the expense ratio, you may pay a trading commission when you buy or sell shares, depending on your brokerage. Many brokerages now offer commission-free trading on ETFs and mutual funds, so check your brokerage's fee schedule before you buy.

Dividends and how they are handled

Many of the 500 companies in the S&P 500 pay dividends — cash payments to shareholders, usually quarterly. When the companies in your fund pay dividends, the fund collects that cash. You then have a choice: reinvest the dividends by buying more shares of the fund, or take the cash as income.

Most S&P index funds offer a dividend reinvestment option. If you choose it, the fund automatically uses your dividends to buy additional shares. Over time, this compounds your returns because you earn dividends on the new shares as well. If you do not reinvest, the dividends are paid to your account as cash, which you can withdraw or use to buy other investments.

The dividend yield of the S&P 500 varies year to year depending on how much cash the 500 companies are paying out. In recent years it has ranged from roughly 1% to 2% annually, meaning a $10,000 investment might generate $100 to $200 per year in dividends.

Tax treatment in taxable accounts

If you own an S&P index fund in a regular taxable brokerage account (not a retirement account), you owe taxes on two things: dividends and capital gains. A capital gain occurs when you sell shares for more than you paid for them.

Because an S&P index fund is passively managed and does not trade stocks frequently, it generates fewer taxable events than an actively managed fund. However, when the index itself changes — when S&P Dow Jones removes a company and adds a new one — the fund must sell the removed stock and buy the new one. This can trigger capital gains that are passed to you as a shareholder.

ETFs are generally more tax-efficient than mutual funds because of how they are structured. ETFs can exchange shares with authorized participants without triggering taxable sales, whereas mutual funds must sell stocks to meet redemptions. If you hold an S&P index fund in a tax-advantaged retirement account like a 401(k) or IRA, you do not owe taxes on dividends or gains until you withdraw money.

How an S&P index fund differs from other index funds

The S&P 500 is one of many stock indexes. Other broad U.S. stock indexes include the Russell 2000 (small-cap companies) and the Nasdaq-100 (technology-heavy large-cap companies). International indexes track stocks outside the U.S., such as the MSCI EAFE Index (developed markets) or the MSCI Emerging Markets Index.

An S&P index fund focuses only on the 500 largest U.S. companies, so it does not include small-cap or mid-cap stocks, and it does not include any international stocks. If you want broader diversification, you might combine an S&P 500 fund with a small-cap index fund or an international index fund. Many investors use an S&P 500 fund as the core U.S. stock holding in a diversified portfolio.

Frequently Asked Questions

Do I own the actual stocks when I buy an S&P index fund?

Yes. The fund holds the actual shares of the 500 companies. You own a fractional share of each company through your ownership of the fund. You do not own them directly — the fund company holds them in your name — but you have a legal claim to your proportional share of the stocks and any dividends they pay.

Can the S&P 500 index fund lose money?

Yes. The fund's value moves with the stock prices of the 500 companies it holds. If those stocks fall in value, your fund loses value. During market downturns, S&P 500 index funds have declined 20%, 30%, or more. However, historically the index has recovered from every downturn and reached new highs over long periods.

What is the difference between an S&P 500 index fund and the S&P 500 itself?

The S&P 500 is a list of 500 companies and their prices — it is not something you can buy directly. An S&P index fund is an investment product that holds those stocks. You buy shares of the fund, not the index. The fund's price per share reflects the combined value of the 500 stocks inside it.

How often does the S&P 500 index change?

Companies are added and removed throughout the year as they meet or fall short of the size and liquidity requirements. On average, about 10 to 20 companies are replaced annually, though this varies. When a change happens, S&P Dow Jones announces it in advance, and index funds adjust their holdings to match.

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

No. An S&P 500 fund holds only the 500 largest U.S. companies. A total stock market index fund (such as one tracking the Wilshire 5000 or Russell 3000) holds thousands of U.S. companies of all sizes, including small-cap and mid-cap stocks. A total market fund is more diversified across company sizes, while an S&P fund is concentrated in large-cap stocks.