India ran, at one point, a weekly index-option expiry on most trading days of the week across two exchanges and several indices. The October 2024 package cut that to one weekly expiry per exchange, on one benchmark index, alongside the monthly and quarterly series that continue for every underlying. The specific index and the specific weekday are exchange decisions and both have changed since, so the count rather than the calendar is the durable fact. One weekly series produces roughly 52 index expiries a year against 12 monthly ones, which is a 4.3-times difference in the number of days on which a book has to be flat or rolled.
The same package carried four other changes worth knowing by name, and each moves a number here. The ₹15 lakh minimum contract size reset the Nifty lot. Option premium must now be collected upfront from buyers. The calendar-spread margin benefit was removed on the expiry day of the expiring leg. And an additional 2% exposure margin was imposed on short option positions on expiry day, which on the covered call in Worked Example 3 adds ₹37,200 to a ₹2,10,550 requirement. That is a 17.7% increase arriving on the one day the position is most likely to be actively managed. All five changes carry verify flags and a date.
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How is the settlement price set?
Then the settlement price itself. Indian index derivatives settle at the volume-weighted average price of the underlying index over the last thirty minutes of the expiry session, not at the last traded price. This is a deliberate anti-manipulation design: a single large order in the closing seconds can move a last price, and it cannot move a thirty-minute volume-weighted average by anything like as much. Stock derivatives settle against the underlying's closing price, computed on the same last-thirty-minute basis.
Three consequences fall out of that convention, and only the first is obvious. A position held to expiry does not settle at the price on the screen at 15:30, so a trader watching the tape in the final minutes is watching the wrong number. An option that is at the money in the last half hour can finish either side of the strike on an average the trader cannot observe in real time. And any strategy whose payoff turns on a fine distinction near the strike, a butterfly's peak or a short strangle's edge, is exposed to a settlement convention rather than to a price.
The price on the screen at the close is not the price you settle at.
How does the US settle index options?
The United States uses different conventions for the same job, and the mismatch is worth carrying. Monthly S&P 500 index options settle against a special opening quotation computed from the opening prices of the constituents on the third Friday, which is a morning number, while the weekly series settles in the afternoon at the close. Two options on the same index, with the same strike, expiring on the same date, can settle against prices set several hours apart.