Stock Indices

S&P 500 (S&P 500 Index)

Standard & Poors 500

An index bundling 500 leading US large-caps by market-cap weight — the most widely used yardstick representing the whole US stock market.

In plain terms

The S&P 500 bundles the stock prices of 500 large companies representing the US into one index. With blue chips like Apple and Microsoft all in it, it is the number most watched for "how the US market did today."

Bundled by market cap (company size), the index moves more when a big company moves. So these days a few giant tech firms can sway the index's direction.

What it tells you

The S&P 500 is like a thermometer of the US economy and market. It is the benchmark for telling whether an individual stock got swept up in the whole market flow or it is just that company.

Countless funds and ETFs worldwide are built to track this index, so the S&P 500 is itself a huge investment target.

Formula

S&P 500 = a market-cap-weighted average of 500 leading US companies
(the bigger the company, the larger its effect on the index)

What high or low means

A rising S&P 500 is read as broad US-market strength, a falling one as weakness. A stock rising more than the index beat the market (outperformed); rising less, lagged.

Whether the index is at an all-time high, and how far it has fallen from a peak (a correction, a bear market), becomes the benchmark for gauging the market mood.

Caution

The S&P 500 is market-cap-weighted, so it skews to a few big companies. The index can rise while most stocks within it struggle, so "index up = all stocks up" is wrong.

Centered on US large-caps, it cannot tell you about small/mid-caps or other countries' markets on its own.

Index quotes are market data. This term is background for understanding market news. (※ Our screen handles individual companies' SEC-filed financials.)

Metrics to read alongside

ETF (Exchange-Traded Fund)

The easiest way to buy the whole S&P 500 is an ETF tracking this index. Knowing the index and the ETF explains what "investing in the whole market" means.

Bull Market / Bear Market

What divides a bull from a bear market is usually the rise or fall of a leading index like the S&P 500 from its peak. Knowing the index lets you read the market phase.

Beta

Beta looks at "how much more that stock swings than the market (usually the S&P 500)." The index is the baseline of that comparison.

See it in real stocks

Search US stocks on Stocklore to see S&P and other financial metrics alongside the sector average.

AAPL Apple Inc.MSFT Microsoft Corporation NVDA NVIDIA Corporation AMZN Amazon.com, Inc.Search stocks →

Exactly how Stocklore computes this metric (formula, thresholds, SEC source) is on the methodology page.

This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.