Guide
What Is a Stock Market Index? A Beginner's Guide
A stock market index is a single number that summarises the performance of a defined group of stocks. Instead of watching thousands of individual prices, you watch one index to gauge how a market — or a slice of it — is doing.
How an index is constructed
An index provider picks a set of stocks by rules (size, liquidity, sector, theme), assigns each a weight, and combines them into one value tracked against a base. Most modern indices are free-float market-cap weighted, meaning a company's weight reflects the market value of its freely tradable shares.
Types of indices
- Broad-market — the whole market or a large-cap slice (NIFTY 50, SENSEX, NIFTY 500).
- Sectoral — one industry (NIFTY Bank, NIFTY IT, NIFTY Pharma), useful for seeing how a sector is doing versus the market.
- Thematic / strategy — built around a theme or factor (dividend, momentum, ESG).
What indices are used for
Indices serve as benchmarks (did my portfolio beat the market?), as the basis for index funds and ETFs, and as the underlying for derivatives. You can explore Indian index levels and their history on the indices pages.