When a news anchor says "the market rose today," they are almost always talking about one thing: the S&P 500. It is the scoreboard for the entire US stock market, the benchmark that professional investors are measured against, and the single investment Warren Buffett has repeatedly told ordinary people to buy. If you understand only one index in your life, make it this one.
What is the S&P 500?
The S&P 500 is a stock market index that tracks the 500 largest publicly traded companies in the United States. Together those 500 companies represent roughly 80% of the total value of the US stock market, which is why the index is treated as shorthand for "the market" as a whole. When people talk about how stocks are doing, this is usually the number they mean.
It is not something you can literally buy. The index itself is just a calculation, a single number that summarizes the combined value of all 500 companies and rises or falls as they do. As of early August 2026, it sat around a record 7,758.
How is the S&P 500 weighted, and which companies dominate it?
The S&P 500 is market-cap weighted, meaning bigger companies carry more influence over the index than smaller ones. A giant like Apple (AAPL) moves the index far more than the 400th-largest member does, even though each counts as one of the 500.
Today that weighting is heavily concentrated in mega-cap technology. The largest holdings include Microsoft (MSFT), Apple (AAPL), Nvidia (NVDA), Amazon and Alphabet, and the top 10 companies alone now make up over 37% of the entire index, one of the highest concentrations on record. The information technology sector by itself accounts for nearly a third of the index. You can see how the biggest names are moving on our market heatmap.
What is the average return of the S&P 500?
Historically, the S&P 500 has returned roughly 10% per year on average over the long run, going back nearly a century. That figure includes brutal crashes and euphoric booms, averaged out across time. More recently, the past decade has been unusually strong, closer to 15% a year.
That 10% long-run average is the engine behind almost every retirement plan, and it is why time in the market matters so much. A 10% annual return doubles your money roughly every seven years through the power of compound interest. Just remember the average hides wild swings; individual years can be up 30% or down 20%.
Why do investors love the S&P 500?
Three reasons make it the default choice for millions of investors. First, instant diversification: one purchase spreads your money across 500 companies and every major sector, so no single failure sinks you. Second, low cost: because the index just holds what it holds, funds that track it charge tiny fees. Third, and most convincing, it beats the professionals. Over long periods, the S&P 500 outperforms the large majority of actively managed funds.
Warren Buffett made this point with money. In 2007 he bet a million dollars that a simple, low-cost S&P 500 index fund would beat a hand-picked basket of hedge funds over ten years. He won in a landslide, and has since told most investors to do exactly that.
How do you invest in the S&P 500?
Since you cannot buy the index directly, you buy a fund that copies it. These come as low-cost index funds or ETFs that hold all 500 stocks in the same proportions, so your money tracks the index almost exactly. The most popular are Vanguard's VOO (VOO), SPDR's SPY (SPY), and iShares' IVV, all of which trade like a normal stock through any brokerage.
For most people, buying one of these on a regular schedule and holding for decades is the entire strategy. If you would rather build around individual names, our stock screener lets you filter the index's members by valuation, growth and dividends.
What are the risks of the S&P 500?
It is diversified, but it is not bulletproof. The biggest risk right now is that record concentration: with the top 10 tech-heavy names making up over a third of the index, a stumble in a few mega-caps can drag the whole thing down, so you are less diversified than 500 companies sounds. It is also US-only, with no international exposure, and it is fully exposed to market crashes; the index has fallen 50% or more in past bear markets and always taken time to recover. Valuation matters too, and you can check how expensive the leaders are using metrics like the P/E ratio.
Bottom line
The S&P 500 is the heartbeat of American investing: 500 of the biggest US companies in one number, historically compounding at around 10% a year. It offers instant diversification at rock-bottom cost and has quietly beaten most professional investors for decades, which is why it is the core holding for so many portfolios. Just go in with open eyes about its heavy tech concentration and its very real crashes, keep buying through the ups and downs, and let time do the work.
