An S&P 500 index fund holds shares in 500 large U.S. companies

An S&P 500 index fund is a fund that owns a piece of 500 of the largest publicly traded companies in the United States. Instead of picking individual stocks, you buy one fund and own a slice of all 500 at once. The fund tracks the S&P 500 index, which is a list of those 500 companies ranked by market value — so the biggest companies make up a larger portion of what you own.

When you buy shares in an S&P 500 index fund, your money is divided among all 500 companies in the same proportions as the index itself. If Apple makes up 7% of the index, then 7% of your money goes toward Apple shares. You do not pick which companies; the fund manager simply mirrors the index.

The fund charges you a fee — usually very small, often less than 0.1% per year — to hold and manage your shares. You pay this fee whether the fund gains or loses money. Some funds charge more than others, so the fee matters over time.

Key Takeaways

  • An S&P 500 index fund owns shares in 500 large U.S. companies and spreads your investment across all of them automatically.
  • You own the companies in the same proportions as the S&P 500 index itself, so the largest companies represent a bigger piece of your fund.
  • The fund charges an annual fee, usually under 0.1%, which is deducted from your account each year.
  • You can buy S&P 500 index funds through a brokerage account, retirement account, or employer retirement plan.

How the fund's value changes

The value of your S&P 500 index fund shares rises and falls with the overall value of those 500 companies. If the companies in the index grow more profitable and their stock prices go up, your fund value goes up. If their stock prices fall, your fund value falls. You do not control this — it depends on how the market values those companies on any given day.

The fund does not try to beat the market or pick winners. It simply owns all 500 companies in fixed proportions. This is called passive investing. You are betting that over time, the largest U.S. companies will grow in value, not that you can pick which ones will outperform.

Where you can buy an S&P 500 index fund

You can buy S&P 500 index funds through most brokerages — firms like Fidelity, Vanguard, Charles Schwab, and others offer them. You open an account, deposit money, and buy shares of the fund just as you would buy a stock. Many funds have low minimum investments, sometimes $1 or even $0 if you set up automatic deposits.

If your employer offers a 401(k) or similar retirement plan, S&P 500 index funds are often one of the investment choices inside that plan. You can also hold them in an IRA or other tax-advantaged retirement account. The account type determines the tax treatment of your gains, not the fund itself.

Different funds track the same index

Multiple companies offer S&P 500 index funds, and they all track the same 500 companies. The difference is in the fee they charge. Vanguard's S&P 500 ETF (ticker: VOO) charges about 0.03% per year. Fidelity's equivalent fund (FXAIX) charges about 0.015%. A fund charging 0.5% per year is much more expensive for the same result.

Over decades, a small difference in fees compounds into a large difference in what you end up with. A fund charging 0.5% instead of 0.1% will cost you thousands of dollars on a $100,000 investment over 30 years. When all the funds own the same 500 companies, the lowest-cost option is usually the best choice.

Why people choose S&P 500 index funds

S&P 500 index funds are popular because they are simple, cheap, and diversified. You own 500 companies with one purchase, so a single company's failure does not wipe out your investment. You do not have to research individual stocks or pay someone else to do it. The fees are transparent and usually very low.

They are also a common choice for long-term investing — retirement accounts, college savings, and other goals where you plan to hold the fund for years or decades. The fund does not require you to make decisions or time the market. You buy it and let it sit.

What you should know about risk

S&P 500 index funds are less risky than owning a single stock, but they are not risk-free. If the overall U.S. stock market falls, your fund falls with it. In 2008, the S&P 500 lost about half its value. In 2022, it fell about 18%. If you need the money in the next few years, a market downturn could force you to sell at a loss.

The fund is designed for people who can leave their money invested through ups and downs. If you might need the money within five years, a stock fund — even a diversified one — may not be the right place for it. Bonds, money market funds, or savings accounts carry less risk but also lower long-term returns.

Dividends and distributions

Many of the 500 companies in the index pay dividends — regular cash payments to shareholders. The S&P 500 index fund collects these dividends and either pays them out to you or reinvests them automatically, depending on which version of the fund you own and how you set it up. Reinvesting dividends means your money stays in the fund and buys more shares, which can increase your long-term returns.

You may owe taxes on dividends even if you do not sell the fund. In a regular brokerage account, you pay tax on dividends each year. In a retirement account like a 401(k) or IRA, you usually do not pay tax until you withdraw the money. This is one reason retirement accounts are popular for index fund investing.

Frequently Asked Questions

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

Unlikely, but theoretically possible only if all 500 large U.S. companies failed simultaneously — which would mean the entire U.S. economy collapsed. More realistically, you can lose a significant portion of your money if the stock market crashes and you are forced to sell before it recovers. This is why time horizon matters: the longer you can hold, the more likely you are to recover from downturns.

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

An ETF (exchange-traded fund) is a type of fund that trades on a stock exchange like a stock. Many S&P 500 index funds are ETFs, but some are mutual funds that you buy directly from the company. The main difference is how you buy and sell them and how they are taxed. Both can track the S&P 500 equally well.

Do I need to pick which S&P 500 fund to buy?

Yes, because different companies offer them at different fees. Compare the annual expense ratio (the percentage fee) across funds at your brokerage. Vanguard, Fidelity, and Schwab all offer very low-cost S&P 500 index funds. Pick the one with the lowest fee available to you, since they all own the same companies.

Should I invest in an S&P 500 index fund or individual stocks?

An S&P 500 index fund is simpler and less risky because you own 500 companies instead of betting on one. Individual stocks can outperform the index, but they can also fail completely. Most people do better with index funds over long periods because they do not require picking winners and they cost less in fees.