Question 1

What is the S&P 500?

Accepted Answer

It is a list of roughly 500 of the largest U.S. companies, picked by a committee at S&P Dow Jones Indices, weighted by market value, and rebalanced four times a year. Apple, Microsoft, Nvidia, JPMorgan, Walmart, all the names you recognize. The index started in 1957 with 500 names; today it usually hovers between 500 and 505 because the math gets fuzzy when companies have multiple share classes. When someone on TV says 'the market was up today,' they almost always mean the S&P 500. It is the default scoreboard for U.S. equities, the benchmark every active mutual fund tries to beat, and the thing your 401(k) target-date fund is probably mostly invested in even if you have never looked.

Question 2

How is the S&P 500 weighted?

Accepted Answer

By market capitalization, which means the bigger a company is, the more it counts. A 1% move in Apple matters about a thousand times more to the index than a 1% move in the smallest member. The top 10 names currently make up roughly a third of the entire index, and the top 50 make up over half. This is why people argue the S&P is no longer really 500 stocks but more like 10 stocks with 490 hangers-on. There is an equal-weighted version of the index that gives every company the same vote, and the gap between the cap-weighted and equal-weighted returns tells you whether the rally is broad or just a handful of giants doing all the work.

Question 3

What is the difference between the S&P 500 and the Dow?

Accepted Answer

The Dow Jones Industrial Average is 30 stocks, weighted by share price, picked by a committee at the Wall Street Journal. The S&P 500 is 500 stocks, weighted by market value, picked by a different committee. The Dow is older, dates to 1896, and has the brand recognition. The S&P 500 is what professional investors actually use because price-weighting is a strange artifact: a $400 stock matters more in the Dow than a $100 stock even if the $100 stock is a much bigger company. If you only have time to look at one number, look at the S&P. The Dow is for the evening news.

Question 4

Can I invest directly in the S&P 500?

Accepted Answer

You cannot buy the index itself; an index is just a calculation. But you can buy a fund that holds all 500 stocks in the same proportions, and these are some of the cheapest, most liquid investments in the world. SPY, IVV, and VOO are the three big ETFs; expense ratios run between 0.03% and 0.09%, which is to say roughly free. Your 401(k) probably offers a Vanguard or Fidelity S&P 500 index mutual fund that does the same thing. Buying the index is the default boring choice that beats most active managers most years, which is the entire reason index investing exists.

Question 5

What is a good S&P 500 return?

Accepted Answer

The long-run average is roughly 10% a year nominal, around 7% after inflation, going back to the 1920s. Any individual year almost never hits that average; the chart looks like a wave, not a line. A great year is plus 25% or better. A normal year is somewhere between 5% and 15%. A bad year is down 10% to 20%. A bear-market year is down 30% to 40%, and you should expect one roughly every decade. The trap is comparing your single year to the long-run average and concluding something is broken when nothing is broken. The average is the average of a wild distribution, not a target the market is trying to hit.

The S&P 500, year by year.

26 years, two bear markets, one straight line up

The S&P 500, answered.

The S&P 500, year by year.

26 years, two bear markets, one straight line up

The S&P 500, answered.

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