What Is the S&P 500 and How to Invest in It

The S&P 500 is the most widely tracked stock market index in the world. When news reports say “the market was up 1.2% today,” they almost always mean the S&P 500 was up 1.2%. When a mutual fund says it “beat the market,” it means it beat the S&P 500. It is the benchmark that everything else in U.S. equity investing is measured against.

Understanding what the S&P 500 actually is — and is not — matters before you put a dollar into it.

What the S&P 500 Actually Is

The S&P 500 (Standard & Poor’s 500) is a market-capitalization-weighted index of approximately 500 of the largest publicly traded companies in the United States, maintained by S&P Dow Jones Indices, a division of S&P Global.

“Maintained by” is important. The S&P 500 is not a mechanical formula that automatically includes any company above a certain market cap. It is managed by an Index Committee at S&P Dow Jones Indices, which uses defined criteria but exercises discretion. Companies must meet all of the following to be eligible:

• Market cap: $20.5 billion minimum (as of 2026 threshold; this is adjusted periodically)
• Domicile: U.S.-incorporated company
• Liquidity: Annual dollar value traded ≥ 1.0× the float-adjusted market cap
• Public float: At least 50% of shares available to the public
• Financial viability: Positive GAAP earnings in the most recent quarter, plus cumulative positive GAAP earnings over the four most recent quarters combined
• Exchange listing: NYSE, NYSE Arca, NYSE American, or Nasdaq

That last earnings requirement is why Tesla was not added to the S&P 500 until December 2020, despite being one of the most valuable publicly traded companies in the world for years before. It did not have four consecutive quarters of GAAP profitability until 2020.

It Is Not Actually 500 Stocks

The S&P 500 contains more than 500 securities. This is because some companies have multiple share classes that are both included — Alphabet (Google) trades as both GOOGL (Class A) and GOOG (Class C) shares, and both are in the index. Berkshire Hathaway similarly. As of early 2026, the index contains approximately 503 securities from ~500 companies.

The index is also not “the 500 largest U.S. companies.” It is roughly that, but the discretionary committee decisions mean some companies that technically meet all criteria are not yet included, and some that fall below the minimum may remain in the index during a grace period. The index is rebalanced quarterly and reconstituted annually.

How Market-Cap Weighting Works

The S&P 500 is market-capitalization weighted, which means larger companies have a larger influence on the index’s performance. A company with a $3 trillion market cap has roughly 100 times the weight of a company with a $30 billion market cap.

This has a significant implication: the S&P 500 is highly concentrated in its largest holdings.

As of early 2026, the top 10 companies in the S&P 500 represent approximately 35% of the entire index. The top 5 companies alone account for roughly 25–27%.

The top 10 holdings as of early 2026 (weights approximate):

Company	Ticker	Approx. Weight
Apple	AAPL	~7.0%
Microsoft	MSFT	~6.5%
Nvidia	NVDA	~6.0%
Amazon	AMZN	~3.8%
Meta	META	~2.6%
Alphabet (Class A)	GOOGL	~2.1%
Alphabet (Class C)	GOOG	~1.8%
Berkshire Hathaway	BRK.B	~1.7%
Broadcom	AVGO	~1.6%
Tesla	TSLA	~1.4%

When someone says they are “broadly diversified” because they own the S&P 500, they have 7% of their money in a single stock (Apple) and nearly 20% in the largest three. That is less diversified than it sounds. It is still diversified relative to owning individual stocks — but investors should understand the concentration.

The heaviest sector weights are Information Technology (~30%), Financials (~13%), and Healthcare (~12%). If the technology sector has a bad decade, the S&P 500 will reflect that heavily.

Historical Returns: The Complete Picture

The S&P 500 has produced approximately 10.7% annualized total returns since 1926 (including dividends reinvested). This is the number cited in most investing literature.

But averages hide the volatility that determines whether you actually capture those returns.

The good years:

• 2013: +32.4%
• 2019: +31.5%
• 2021: +28.7%
• 2023: +26.3%
• 2024: +23.3%

The bad years:

• 2008: -37.0% (financial crisis)
• 2002: -22.1% (dot-com bust, post-9/11)
• 2022: -18.1% (rate hike cycle)
• 2020: -34% peak-to-trough (COVID crash, though the year ended +18.4%)
• 2001: -11.9%

The -37% year in 2008 is the number every new investor needs to internalize before putting money in. A $100,000 portfolio would have been worth $63,000 by the end of 2008. It would have taken until April 2013 — four and a half years — to recover to $100,000 in nominal terms. In real (inflation-adjusted) terms, the recovery took even longer.

This does not mean the S&P 500 is a bad investment. Over long enough periods, it has rewarded patient investors. But the journey includes sustained multi-year periods of losses, and investors who cannot handle those periods and sell at the bottom lose both ways — the decline and the recovery.

Long-run performance by decade:

• 1930s: -5.3% annualized (Great Depression)
• 1940s: +9.2%
• 1950s: +19.4%
• 1960s: +7.8%
• 1970s: +5.9% (stagflation)
• 1980s: +17.5%
• 1990s: +18.2%
• 2000s: -0.9% (the “lost decade” — two major crashes)
• 2010s: +13.6%
• 2020–2024: ~14.6%

The 2000s decade is particularly sobering. An investor who retired at the start of 2000 with all their savings in the S&P 500 would have watched it go roughly nowhere for 10 years before factoring in inflation — which means they lost purchasing power in real terms. Sequence-of-returns risk is real, and pure S&P 500 exposure is not appropriate for everyone at every stage of life.

How to Invest in the S&P 500

The three primary vehicles for retail investors:

ETFs (Most Flexible)

The majority of retail investors buy S&P 500 exposure through Exchange-Traded Funds (ETFs), which trade on exchanges like stocks and can be bought and sold throughout the trading day.

ETF	Provider	Expense Ratio	AUM	Dividend Yield (approx.)
VOO	Vanguard	0.03%	~$600B	~1.3%
SPY	State Street	0.09%	~$560B	~1.3%
IVV	iShares (BlackRock)	0.03%	~$540B	~1.3%
SPLG	State Street	0.02%	~$60B	~1.3%
FXAIX	Fidelity (mutual fund)	0.015%	~$650B	~1.3%

VOO vs SPY: Both track the S&P 500 precisely. The difference is expense ratio (0.03% vs 0.09%) and structure. SPY is a unit investment trust (a legacy legal structure from 1993 when it launched as the first U.S. ETF) and must hold cash dividends rather than reinvesting them immediately. This creates a small performance drag called “dividend drag.” VOO and IVV do not have this constraint.

Over 30 years, the 0.06% expense ratio difference between VOO and SPY compounds to meaningful money. On a $500,000 portfolio, you save approximately $3,000/year in fees with VOO. Over 30 years at 8% returns, that difference compounds to roughly $340,000 in ending portfolio value. SPY’s primary advantage is liquidity — its bid-ask spread is tighter than any other equity ETF, which matters for large institutional traders but is irrelevant for a retail investor buying $500 at a time.

The practical recommendation: For long-term buy-and-hold investors, VOO or IVV at 0.03% expense ratio is the right choice. SPY’s higher expense ratio is justified only for institutional hedgers who need extreme liquidity.

SPLG (SSGA’s low-cost S&P 500 ETF at 0.02%) is the cheapest option but significantly less liquid. Fine for buy-and-hold; not ideal for active trading.

FXAIX is technically a mutual fund, not an ETF — available only at Fidelity. At 0.015% expense ratio, it is the cheapest S&P 500 index product available, but mutual funds trade only once per day at NAV rather than intraday like ETFs.

Mutual Funds

If you invest through a 401(k) or IRA at a single custodian, you may have access to mutual fund versions of S&P 500 index funds. Vanguard’s VFIAX (0.04% expense ratio, $3,000 minimum), Fidelity’s FXAIX (0.015%, no minimum), and Schwab’s SWPPX (0.02%, no minimum) are the most common options.

Index Annuities (Avoid)

Some insurance products claim to offer “S&P 500 returns with no downside risk.” These indexed annuities capture only part of the upside (via participation rates and caps, often 8–12% maximum annual gain) while collecting fat insurance company fees. They are not a substitute for direct S&P 500 index fund ownership. The costs hidden inside these products routinely exceed 2–3% annually, destroying most of the index return they claim to offer.

Why the S&P 500 Is Not a Complete Portfolio

For most investors under 50 with long time horizons, the S&P 500 is an appropriate core holding — but it is not a complete portfolio by itself.

What it excludes:

• International stocks: The S&P 500 is 100% U.S. companies. International developed markets (Europe, Japan, Australia) and emerging markets (China, India, Brazil) represent roughly 60% of global market capitalization. U.S. stocks have outperformed international stocks for the past 15 years, but that is not a law — there have been extended periods where international markets outperformed the U.S.
• Small and mid-cap stocks: The S&P 500 covers large caps only. Small and mid-cap stocks have historically offered higher long-run returns with higher volatility. A total market fund (VTI, ITOT) captures small and mid caps alongside large caps.
• Bonds and other assets: Pure equity exposure is appropriate for long time horizons, but becomes less appropriate as retirement approaches. A portfolio containing only the S&P 500 will experience the full -37% drawdown in a 2008-style event.
• Real assets: REITs, commodities, and inflation-linked bonds offer diversification that pure equity exposure does not.

The S&P 500 is an excellent building block. For investors who want simplicity and discipline, a single S&P 500 ETF bought consistently over decades is a legitimate wealth-building strategy. But understanding its composition — heavily concentrated in large-cap U.S. technology companies — helps you make an informed choice about whether it is the right fit for your full portfolio.

Tax Considerations

Taxable accounts: S&P 500 index ETFs are highly tax-efficient. The structure of ETFs allows most index funds to distribute little or no capital gains in most years. Dividends from VOO, SPY, and IVV are typically qualified dividends, taxed at the preferential 0%/15%/20% rate rather than ordinary income rates. This makes them efficient holdings in taxable brokerage accounts.

Tax-advantaged accounts: If you have room in an IRA or 401(k), S&P 500 index funds are appropriate there as well — though their inherent tax efficiency makes them somewhat less critical to shelter compared to high-dividend assets or bond funds, which generate more ordinary income.

Selling shares: When you eventually sell, each purchase creates a separate tax lot. If you hold for longer than one year, gains are taxed at long-term capital gains rates. If you hold less than one year, gains are taxed as ordinary income. For index fund investors with decade-long horizons, this distinction matters mostly at the time of liquidation.

The Bottom Line

The S&P 500 has delivered approximately 10.7% annualized returns since 1926 — one of the most powerful long-run return engines available to retail investors. The vehicles to access it (VOO, IVV, FXAIX) charge as little as 0.015% annually.

Understanding the full picture — the concentrated tech exposure, the lost decades, the -37% drawdowns — does not change the long-term case. It changes how you hold it psychologically. Investors who understand what they own do not panic-sell in 2008 or 2020. They buy more.

For a deeper dive on how ETFs work mechanically, read our guide on what is an ETF. If you are deciding between the S&P 500 and a total market fund, our VOO vs VTI comparison covers the differences in detail.