What is a stock market index (S&P 500, FTSE MIB)
A stock market index is a number that summarizes the performance of a group of companies, like a market thermometer. Instead of watching stock by stock, the index tells you whether "the market" as a whole is rising or falling.
The most famous indices
The S&P 500 gathers the 500 largest listed companies in the US: when you hear it mentioned, it's a snapshot of the American stock market. The FTSE MIB does the same for Italy, with the top 40 companies on the Milan exchange. Other famous ones: the Nasdaq (US tech) and the Dow Jones.
If the news says "the Milan stock exchange closed up 1%", they're talking about the FTSE MIB.
Why it's useful to you
The index is a benchmark: it tells you how an entire market is doing without having to follow hundreds of stocks. And it's also investable: many ETFs replicate an index, so with one purchase you "buy" all the companies in it.
Example: by buying an ETF on the S&P 500, your investment rises or falls along with the 500 largest US companies, automatically.
In short
- An index summarizes the performance of a group of companies in a single number.
- S&P 500 = large US companies; FTSE MIB = leading Italian companies.
- It's the "thermometer" for understanding how a market as a whole is doing.
- Many ETFs replicate an index: you invest in it with a single purchase.
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Educational content only. MarketMind explains what happens and why; it never gives investment advice. Read this guide in Italian.