Sensex
India's oldest equity benchmark — the BSE's 30-stock barometer and the underlying for BSE's Friday-expiry weekly options contract.
Definition
Sensex (short for Sensitive Index) is the flagship equity index of the Bombay Stock Exchange (BSE), comprising 30 large-cap, liquid, and financially sound companies across major sectors of the Indian economy. Launched in 1986 with a base value of 100 as of April 1, 1979, it is India's oldest continuously published stock market index and carries significant symbolic weight in global financial reporting. The index is free-float market-capitalisation weighted and is reviewed periodically by the BSE Index Committee. It forms the underlying for BSE's futures and options contracts, with weekly expiry on Fridays and monthly expiry on the last Friday of the month. The lot size for Sensex derivatives is 10 units.
Why it matters
Despite Nifty 50 being the dominant F&O benchmark domestically, Sensex remains the index most commonly referenced in international media when reporting on India's equity market, making it a key sentiment gauge for foreign institutional investors (FIIs). With SEBI's 2023 rationalisation of weekly expiries — which retained only one weekly contract per exchange — BSE retained Sensex as its surviving weekly product, and BSE's Sensex and Bankex options have since seen substantial volume migration from NSE's discontinued weekly contracts. For options traders, the Friday expiry creates a distinct strategy window: Sensex positions can be set on Thursday evening to capture Friday's gap-open and intraday move, capturing or hedging weekend risk. The 10-unit lot size at a high index level implies a meaningful notional value per lot, making margin requirements non-trivial and position sizing discipline essential. STT (Securities Transaction Tax) applies to options on exercise and applies to the full intrinsic value on expiry for in-the-money contracts — a meaningful cost for those holding deep ITM options into Friday close.
How it works
Sensex is calculated in real time from 9:15 AM to 3:30 PM IST on BSE trading days using the free-float adjusted market capitalisation of its 30 constituents. The formula divides the current aggregate free-float market cap of constituents by a base market cap figure and multiplies by the base index value of 100 to produce today's level. BSE's index maintenance team applies corporate action adjustments (splits, bonuses, rights) through divisor changes to ensure continuity. Sensex options are European-style and cash-settled. The final settlement price on expiry Friday is derived from the closing Sensex value as reported by BSE.
Example
Suppose Sensex is hypothetically trading near 80,000 on a Thursday afternoon and a macro event (say, a US Fed statement) is expected on Friday morning. A trader buys a 79,500 PE expiring the next day at a hypothetical premium of ₹120 per unit, paying ₹1,200 in total (10 units per lot) as downside protection. If Sensex falls to a hypothetical 78,800 by Friday's close, the PE is worth ₹700 (intrinsic value of 79,500 − 78,800), netting a profit of ₹700 − ₹120 = ₹580 per unit before STT and brokerage. These figures are purely illustrative and not a recommendation to trade.
Watch Sensex options data in real time
TradePulse tracks Sensex strikes, OI shifts, and PCR live so you can spot Friday-expiry positioning as it develops.