Synthesizing Macro Events with Expiry

Start with expiry day alone. An option has two parts to its price: intrinsic value (what it is worth if exercised now) and time value (what you pay for the chance that it becomes valuable). On the last day time value is almost gone, so the price depends almost fully on where the index finishes compared with the strike. Gamma is the Greek that measures how fast an option's delta (its sensitivity to the index) changes. Near the strike on expiry day gamma is very high: a small move in the index can turn an option from nearly worthless to valuable, or the reverse.

Now add an event. Normally implied volatility (IV) falls as expiry nears, because time value fades. If a major announcement is still to come, traders keep paying extra for at-the-money options until the news is out. After it, the extra charge can vanish within minutes. This is why an event-day option can lose value even when the index moves in your direction: the premium was carrying a charge for uncertainty that has now been removed.

The exchange calendar has changed recently. Since September 2025, weekly index contracts exist for only one index on each exchange (Nifty 50 on NSE, Sensex on BSE), and each exchange fixes one expiry weekday. Confirm the current weekday on the exchange contract page, because it can be revised. So a clash day is not a fixed day of the week: check the exchange calendar and the macro calendar side by side.

Some large sellers of options protect themselves by trading the index or futures as prices move. If a seller has sold many puts and the market falls through their strike, their delta grows and they may need to sell more of the underlying to stay protected. That selling can push prices down further. Traders call this a gamma effect. It is a real mechanism in theory, and it can help explain why some sharp moves accelerate near heavily traded strikes.

Now the limits. You cannot see who holds each position. Open interest (OI) on the option chain is the number of contracts outstanding, but it does not say whether a large holder is long or short, or whether they are hedged elsewhere. So a big number at a strike is a hint, not proof. Also, market makers and large institutions hedge in different ways, and regulators now watch intraday positions in index options closely.

A fair way to use this idea is as a reason for caution, not as a signal. Around a big strike on a clash day, fast moves are possible. That is a reason to use smaller size and defined risk, and not a reason to bet on a breakout or a pin.

The aim of a checklist is to make decisions in advance, when you are calm. You are not trying to forecast the news. You are deciding how much you can afford to be wrong and how you will behave when prices jump.

The comparison below shows why buyers and sellers face different risks. Neither side is safer in an absolute sense: the buyer risks a smaller, known amount often, the seller earns small amounts often and risks a larger amount rarely.