S&P 500 vs Dow Jones vs Nasdaq-100: how the three indices differ

When someone says “the market is up,” they might mean one of three indices — and the answer changes the picture. The S&P 500, the Dow Jones Industrial Average, and the Nasdaq-100 are the three most quoted U.S. stock indices. They measure different slices of the market and they do it in different ways.

Quick comparison

• S&P 500 — 500 large U.S. companies across all sectors, weighted by market cap.
• Dow Jones Industrial Average (DJIA) — 30 blue-chip U.S. companies, weighted by share price.
• Nasdaq-100 — 100 largest non-financial companies listed on the Nasdaq exchange, weighted by market cap.

The S&P 500

Launched in 1957 in its current form, the S&P 500 is the broadest and most representative of the three. It covers roughly 80% of U.S. equity market cap and spans all 11 GICS sectors. For most investors and fund managers, it's the default benchmark.

If you want a primer, see our guide to the S&P 500.

The Dow Jones Industrial Average

The Dow is the oldest of the three — Charles Dow launched it in 1896 with just 12 companies. Today it tracks 30 large U.S. companies hand- picked by the editors of the Wall Street Journal and S&P Dow Jones Indices. The components are chosen to be “leaders in their industries,” not by any mechanical rule.

The Dow has one quirky feature: it is price-weighted, not market-cap-weighted. A $400 stock moves the Dow more than a $50 stock, even if the $50 stock's company is ten times larger. This is widely considered an outdated methodology — but the Dow's historical brand keeps it in the headlines.

The Nasdaq-100

The Nasdaq-100 was launched in 1985. It contains the 100 largest non-financial companies listed on the Nasdaq stock exchange. Because Nasdaq is historically the home of technology listings, the index is heavily tech-weighted — well over 50% Information Technology and Communication Services in most years.

It is market-cap weighted with a special rebalancing mechanism that prevents any single company from dominating. The Nasdaq-100 is the index behind QQQ, one of the most actively traded ETFs in the world.

How they overlap

These indices are not mutually exclusive. The biggest U.S. tech companies — Apple, Microsoft, Nvidia, Alphabet, Amazon, Meta — appear in all three. That overlap means the three indices often move together, especially on days when mega-cap tech moves.

Where they diverge:

• Energy and financials.Heavily represented in the S&P 500 and the Dow, basically absent from the Nasdaq-100.
• High-priced industrial stocks.Stocks like UnitedHealth or Goldman Sachs sway the Dow a lot because of share price, but matter much less in the S&P 500.
• Mid-cap tech.Visible in the Nasdaq-100, diluted inside the broader S&P 500.

Which one should you watch?

For a sense of the overall U.S. market: the S&P 500. It's the most representative single number.

For a read on the technology and large-cap growth story: the Nasdaq-100.

For news headlines and very long-term comparisons: the Dow. It's the most-watched ticker but the least statistically defensible benchmark.

One more index worth knowing

The Russell 2000tracks small-cap U.S. companies. It captures the part of the market the other three indices ignore. When people talk about “small caps lagging mega-caps,” this is usually the comparison they mean.

The bottom line

Think of the three indices as different lenses on the U.S. market. The Dow is a curated brand. The Nasdaq-100 is a tech-tilted slice. The S&P 500 is the broad, methodical benchmark — which is why most professional investors anchor their thinking to it.