Glossary · Options
Expiry Day
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Expiry day is the final trading day of a derivatives contract — the day a futures or options contract settles and ceases to exist. On NSE, index options settle in cash against the closing settlement value of the underlying index: in-the-money options are settled at their intrinsic value, and out-of-the-money options expire worthless. NIFTY has weekly and monthly expiries, each falling on its designated weekly expiry day; exact expiry weekdays have been revised by exchanges over time, so check the current NSE contract calendar rather than assuming.
Expiry sessions have a distinct character: theta decay is at its steepest, premiums near the money can evaporate or explode within minutes, and gamma is extreme — small index moves produce violent option P&L swings late in the day.
Example
On a weekly expiry day, NIFTY trades at 25,020 near the close. The 25,000 call settles worth its intrinsic value of about ₹20; the 25,100 call, worth ₹35 in the morning, expires at zero. A buyer of one lot (75) of that 25,100 call loses the full 35 × 75 = ₹2,625 premium; the seller keeps it. Hypothetical figures — expiry-day option selling carries its own tail risk when the index moves sharply.
Why it matters
Expiry is a regime, not just a date. Strategies tuned on ordinary sessions often misbehave on expiry day, so systematic traders either build expiry-specific rules (entry times, tighter stops, earlier exits) or exclude expiry sessions entirely — and backtests should separate expiry-day performance from the rest to see which.
In INDfolio AI, options strategies can be backtested with expiry-aware logic on NSE data — see Options backtesting.