"The market was up today" usually gets summarized with one of three numbers — the S&P 500, the NASDAQ, or the Dow Jones. They frequently move together, but they're measuring genuinely different things, and mixing them up leads to real misunderstandings about what's actually happening.
S&P 500: the broad benchmark
The S&P 500 tracks 500 of the largest publicly traded U.S. companies, weighted by market capitalization — bigger companies move the index more than smaller ones. It's the closest thing to a general "how is the U.S. stock market doing" number, and it's what most index funds and retirement accounts are benchmarked against.
NASDAQ Composite: tech-heavy by construction
The NASDAQ Composite includes every company listed on the Nasdaq exchange — thousands of them — but because Nasdaq is where most major tech companies list, the index is heavily weighted toward technology and growth stocks. This is why the NASDAQ often swings harder than the S&P 500 in either direction: it's a less diversified, more sector-concentrated number.
Dow Jones: 30 companies, priced differently
The Dow Jones Industrial Average tracks just 30 large companies, and — unusually — it's price-weighted, not market-cap weighted. That means a $500 stock moves the Dow more than a $50 stock, regardless of which company is actually bigger. This quirk, left over from how the index was originally calculated in 1896, is part of why financial commentators generally consider the S&P 500 a more meaningful gauge despite the Dow getting more headline attention.
Why they sometimes disagree
A day where tech stocks sell off but industrial and consumer stocks hold steady can show the NASDAQ down sharply while the Dow barely moves — same market, different lens. Watching more than one index at once gives a clearer picture than any single number.
Watch them together
The Stock Market Indices Tracker shows the S&P 500, NASDAQ, Dow, and 24 other major indices from around the world side by side, so you can see the fuller picture in one place instead of piecing it together from headlines.