Sensex

The Sensex (Sensitive Index) is the benchmark equity index of the Bombay Stock Exchange (BSE), comprising 30 well-established, financially sound companies across key sectors of the Indian economy. It was introduced on 1 January 1986, with a base year of 1978-79 and a base value of 100, making it one of Asia's oldest stock indices.

The Sensex is calculated using the free-float market capitalisation method — only the shares available for public trading (excluding promoter holdings, government holdings, and strategic stakes) are considered. Each constituent's weight is proportional to its free-float market cap relative to the total. As a result, heavyweights like Reliance Industries, TCS, HDFC Bank, and Infosys disproportionately influence the index movement.

The 30 companies in the Sensex are selected based on listing history, trading frequency, market cap rank, and sector representation. The index committee reviews composition semi-annually. Entry into the Sensex is considered a badge of market relevance — companies added to the index often see buying pressure from index funds and ETFs that track it.

While the Nifty 50 has become the primary benchmark for derivatives trading and institutional reference, the Sensex retains its importance as India's most widely quoted market indicator in mainstream media. When news anchors say "the market fell 500 points," they typically mean the Sensex. Its longer history also provides a richer dataset for long-term market analysis.

The Sensex's journey from 100 in 1979 to over 70,000 in recent years reflects India's economic transformation — from a closed, license-raj economy to one of the world's largest and fastest-growing markets. Major milestones include crossing 1,000 (1990), 10,000 (2006), 50,000 (2021), and each successive milestone arriving faster than the last, illustrating the power of compounding economic growth.