Anatomy of Expiry Day Trading

Two plain terms first. An option’s premium has two parts: intrinsic value (what it would pay if used right now) and time value (the price of the chance that it will be worth more later). The buyer of an option pays the premium. The seller receives it and takes on the obligation.

On expiry day, time value runs out. By the final settlement, an option is worth only its intrinsic value. If the index is at 24,600 at expiry, a 24,500 call is worth 100 points and a 24,500 put is worth nothing. The buyer of the call receives ₹100 per unit in cash. The seller of that call pays ₹100. The put expires worthless: its buyer loses the premium paid, its seller keeps it.

For NIFTY and other index options, settlement is in cash, and the option is European style, meaning it can be used only at expiry. Stock options are different: they settle by delivery of shares. Check the current rule for the contract you trade.

As of the latest notices we could confirm, NSE runs weekly expiry only on NIFTY, and it falls on a Tuesday. Bank Nifty has monthly expiry, on the last Tuesday of the month. BSE’s weekly expiry for Sensex is on Thursday. These days changed in September 2025 and may change again. Confirm on the exchange website before you rely on any day.

Near the end of the day, an option close to the index level has a small premium, maybe a few rupees. But its final value is either zero or the number of points it ends in the money. A small move of the index can therefore turn a tiny premium into several times its size, or wipe it out. This sensitivity is called gamma. Close to expiry, gamma is highest for options near the index level.

Theta is the loss of time value as the hours pass. On expiry day, theta is at its fastest, because whatever time value is left must go to zero by the close. This favours sellers if the index stays still and hurts buyers. If the index moves, the same sensitivity works against sellers and helps buyers.

Illustration of the sellers’ problem. A seller of a 24,500 call receives ₹5 with the index at 24,480. If the index rises to 24,540, the seller owes 40 and the loss is 40 − 5 = ₹35 per unit, or 35 × 65 = ₹2,275 per lot. For a buyer of that call, the premium was ₹5 per unit, so the most the buyer loses is 5 × 65 = ₹325 per lot. The seller’s loss is limited only by how far the index goes.

Neither position is “the right one”. The buyer pays a small amount for a rare, large payoff. The seller earns a small amount, often, and takes a rare, large loss. Which fits depends on your capital, costs and how much loss you can accept. The arithmetic does not favour either automatically.

The two sides of an option are not equal in what they risk. The exchange also knows this. Since late 2024, SEBI and the exchanges have introduced several measures on index derivatives, including collecting option premium upfront from buyers, one weekly expiry per exchange, and extra margin on expiry day for sold options. Exact rates and dates have been revised. Needs verification on the exchange and SEBI websites before you rely on any of them.

Market makers, who quote prices on both sides, try to stay balanced by hedging. Their hedging can add to trading volume near expiry. But you cannot see their books. A story such as “big players will push the index to a certain level” is a guess, not a fact from the chain.

The takeaway: expiry day is a day when small moves count for a lot. That makes it exciting and also expensive to be wrong. SEBI’s own studies of individual F&O traders, including the one reported for FY26, found that most lost money. Needs verification of the FY26 figures against the SEBI publication itself. A sound approach is to size positions so that a full loss on expiry day is a small part of your capital.