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The S&P 500 Is Not a Mutual Fund—Here's What It Actually Is

By Adrian Watts · Stocks and Funds Writer

The S&P 500 is an index, not a mutual fund

The S&P 500 is a list of 500 large American companies, ranked by market value. It is not itself a mutual fund. You cannot buy "the S&P 500" the way you buy a mutual fund. What you can buy are mutual funds and exchange-traded funds (ETFs) that track the S&P 500—meaning they hold the same 500 stocks in roughly the same proportions, so their performance mirrors the index.

The confusion is understandable. Financial news constantly refers to "the S&P 500 is up today" or "the S&P 500 closed at X." These statements describe the index itself, which is a measurement tool, not an investment product. The index is maintained by S&P Dow Jones Indices, a division of S&P Global, and it exists to show how the largest U.S. companies are performing as a group.

Key Takeaways

  • The S&P 500 is a benchmark index of 500 large U.S. companies, not an investment product you can purchase directly.
  • You invest in the S&P 500 by buying a mutual fund or ETF that tracks the index, which holds all or most of those 500 stocks.
  • S&P 500 index mutual funds charge lower fees than actively managed funds because they simply replicate the index rather than trying to beat it.
  • Both mutual funds and ETFs track the S&P 500, but they differ in how you buy them, when you can trade them, and their tax treatment.

How S&P 500 index funds work

An S&P 500 index mutual fund holds all 500 stocks in the index. When you buy shares of the fund, you own a small piece of all 500 companies at once. The fund manager's job is straightforward: buy and hold the stocks in the index, rebalance when the index changes, and keep costs low.

Because the fund is simply copying the index rather than trying to beat it, the fund's return will closely match the index's return—minus the fund's fees. A fund that charges 0.03% per year will return almost exactly what the S&P 500 returns. A fund that charges 0.50% per year will lag the index by roughly that amount.

This is different from an actively managed mutual fund, where a manager picks individual stocks they believe will outperform the market. Those funds charge higher fees—often 0.50% to 1.50% or more—because they require research and decision-making. S&P 500 index funds are cheaper because the strategy is mechanical.

Mutual funds versus ETFs that track the S&P 500

Both mutual funds and ETFs can track the S&P 500, but they work differently. A mutual fund is bought and sold directly through the fund company or a brokerage, and the price is set once per day after the market closes. You place an order during the day, but you do not know the exact price until that evening.

An ETF trades on a stock exchange like a stock does. You can buy and sell it any time the market is open, and the price changes throughout the day. ETFs typically have lower expense ratios than mutual funds tracking the same index, though the difference has narrowed in recent years.

For most individual investors, the choice between an S&P 500 index mutual fund and an S&P 500 ETF comes down to how you like to trade and which one your brokerage makes easiest to buy. Both will give you exposure to the same 500 companies at a low cost.

Common S&P 500 index funds and ETFs

Vanguard offers the Vanguard 500 Index Fund (mutual fund) and the Vanguard S&P 500 ETF (ticker VOO). Fidelity offers the Fidelity 500 Index Fund and the Fidelity S&P 500 ETF (ticker FXAIX and FXAIX, respectively). Schwab offers the Schwab S&P 500 ETF (ticker SWPPX). Each holds the same 500 stocks and charges a very low annual fee—typically between 0.03% and 0.10%.

The specific fund you choose matters far less than the expense ratio and whether your brokerage makes it easy to buy. If you have a 401(k) through your employer, your plan likely offers at least one S&P 500 index option. If you are opening a brokerage account on your own, nearly every major broker offers multiple choices.

Why people confuse the S&P 500 with a mutual fund

The S&P 500 is so widely discussed in financial news that it feels like a thing you can own. When a news anchor says "invest in the S&P 500," they are speaking loosely. What they mean is "invest in a fund that tracks the S&P 500." The index itself is just a number—a way of measuring the market.

The index is also used as a benchmark. Financial advisors compare the performance of mutual funds and other investments against the S&P 500 to see whether they are beating or lagging the broader market. This constant comparison reinforces the idea that the S&P 500 is a thing you can buy, when really it is a standard you can measure against.

When an S&P 500 index fund makes sense in a portfolio

An S&P 500 index fund or ETF is often a core holding for investors who want broad exposure to large U.S. companies without paying high fees or spending time picking individual stocks. Because it holds 500 companies across many industries, it provides diversification within a single fund.

Many financial advisors recommend S&P 500 index funds as a foundation for long-term investors, particularly in retirement accounts like IRAs and 401(k)s. The low fees mean more of your money stays invested and compounds over time. Over decades, that difference compounds significantly.

An S&P 500 index fund is not a complete portfolio by itself—it only covers large U.S. companies—but it is often the largest piece of a diversified portfolio that might also include small-cap stocks, international stocks, bonds, or other asset types.

Frequently Asked Questions

Can I buy the S&P 500 directly?

No. The S&P 500 is an index, not an investment product. You buy a mutual fund or ETF that tracks the index. The fund holds the 500 stocks, and you own shares of the fund.

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

Both hold the same 500 stocks and track the same index. The main differences are how you buy them (mutual funds trade once daily; ETFs trade throughout the day like stocks), their expense ratios (ETFs are often slightly cheaper), and tax treatment (ETFs are often more tax-efficient). For most investors, the choice is minor.

Will an S&P 500 index fund match the index exactly?

Almost, but not quite. The fund's return will lag the index by roughly its annual expense ratio. A fund charging 0.05% per year will return about 0.05% less than the index. This is called tracking error, and it is normal and expected.

Is an S&P 500 index fund a good investment for beginners?

Yes, for many beginners. It provides instant diversification across 500 large companies, charges very low fees, and requires no stock-picking skill. It is a simple way to own a piece of the U.S. stock market. However, it should typically be part of a broader portfolio that may include other asset types.