JustChartsWhat Is the S&P 500 (SPX / US500)? How the Index Works
The S&P 500 is a stock index of about 500 of the largest US companies, weighted by their float-adjusted market value, so the biggest companies have the most influence. It covers roughly 80% of the US stock market’s value. Traders access it through E-mini futures (ES, $50 per point), micro futures (MES, $5 per point), ETFs and CFDs often named US500 or SPX500.
Key facts
- Companies
- about 500 large US companies
- Weighting
- float-adjusted market capitalisation
- Launched
- 1957
- E-mini futures (ES)
- $50 per index point
- Micro E-mini (MES)
- $5 per index point
How the S&P 500 is calculated
Each company’s weight depends on the market value of its shares available to the public. A company worth ten times another has about ten times the influence on the index. That makes the S&P 500 heavily influenced by its largest technology companies.
A committee at S&P Dow Jones Indices chooses members based on size, liquidity, profitability and sector representation, so it is not simply the 500 largest companies.
S&P 500 vs the Dow and Nasdaq 100
| Index | Companies | Weighting |
|---|---|---|
| S&P 500 | ~500 large US companies | Market value |
| Dow Jones (US30) | 30 large US companies | Share price |
| Nasdaq 100 | 100 largest non-financial Nasdaq companies | Modified market value |
Trading hours
- Cash index: 9:30 a.m.–4:00 p.m. New York time.
- Futures and most US500 CFDs: nearly 24 hours, Sunday evening to Friday afternoon New York time, with a daily break around 5:00–6:00 p.m.
What moves the S&P 500
- Earnings, especially from the largest companies.
- Interest rates and Fed decisions — see FOMC and CPI.
- Economic data such as NFP and GDP.
- Risk sentiment — its options market sets the VIX.
Frequently asked questions
Is US500 the same as the S&P 500?
US500 is a name brokers use for CFDs that track the S&P 500, usually priced off the futures market.
How many companies are in the S&P 500?
About 500 companies, though the count of share classes is slightly higher because some companies have more than one listed share class.
How much is one point on the S&P 500 worth?
$50 on an E-mini future, $5 on a Micro E-mini, and a broker-defined amount (often $1 per lot) on a CFD.
Put it into practice
Live charts, an economic calendar and trading calculators — free with a JustCharts account.
Open the live S&P 500 chartThis article is for education only and is not financial advice. Trading leveraged products carries a high risk of losing money. Contract sizes, trading hours and leverage limits vary by broker and country — always check your own broker’s specifications.