Expiry day is not a normal trading day with a deadline attached. It is a day on which option behaviour changes character, because the mathematics that price options behave differently when almost no time remains.
This guide covers what actually changes, why index options settle in cash rather than delivery, and what that means for building strategies that run on or near expiry.
What actually changes near expiry
The Greeks explain all of it. If you have not read the Greeks guide, the short version is that they measure how an option's price responds to price, time and volatility.
| Greek | What it does near expiry | Consequence |
|---|---|---|
| Theta | Decay accelerates | Premium erodes fast — good for sellers |
| Gamma | Rises sharply at the money | Delta flips quickly — dangerous for sellers |
| Vega | Falls towards zero | Volatility changes matter less |
| Delta | Becomes binary near the strike | An option is nearly 1 or nearly 0 |
The first two rows are the whole story of expiry-day option selling, and they pull in opposite directions. You are paid faster and you are carrying a position that can turn against you faster. The attraction and the danger are the same mechanism.
Why delta becomes binary
Away from expiry, an option's delta changes smoothly as the index moves. With hours left, that smoothness disappears.
An option a hundred points out of the money with a week left still has a real chance of finishing in the money, so it carries meaningful delta. The same option with twenty minutes left has almost no chance, so its delta collapses towards zero. An option just in the money has delta approaching one, because it will almost certainly stay there.
What that means for a position
The practical consequence: around the strike, small index moves produce large changes in your position's exposure. A short option that was comfortably out of the money can become a near-certain loss in the time it takes the index to move fifty points.
Cash settlement
Index options in India settle in cash. There is no delivery of anything — the index is a number, not a tradeable basket you could receive.
At expiry, an in-the-money option is settled against the index's settlement value, and the difference is credited or debited to your account. An out-of-the-money option simply expires worthless.
Why this simplifies things
This matters practically: you do not need to square off an out-of-the-money position to avoid an obligation, because there is no obligation to avoid. You may still choose to, for reasons below.
The settlement value is not the last price
The settlement value is calculated by the exchange using a defined method rather than simply the last traded price. The exact method is published by the exchange, and it is worth knowing it is not necessarily the closing tick you watched.
Should you hold to expiry or square off?
A genuine decision rather than a formality, and it has arguments on both sides.
| Holding to expiry | Squaring off before |
|---|---|
| No exit cost — the option simply expires | Pays the spread and charges on the way out |
| Captures the last of the premium | Gives up the final decay |
| Exposed to a late move through your strike | Removes that risk entirely |
| Settlement value may differ from the last price you saw | You know exactly what you got |
For a position comfortably out of the money, holding is usually reasonable and saves the exit cost. For a position near the strike, the last hour carries risk that is disproportionate to the premium still available.
A workable rule
A defensible default: square off anything near the money, hold what is clearly out of it. Whichever you choose, decide it in advance and encode it as an exit time rather than improvising at 15:20.
Why expiry-day strategies are popular
Accelerating decay is genuinely attractive to a seller. A position opened in the morning and closed in the afternoon captures a disproportionate share of the remaining premium, because that is when decay is fastest.
The structures that exploit this are the familiar ones — short straddles and strangles near the money, where the decay is concentrated.
What the popularity obscures
What the popularity obscures is that the same strikes carry the most gamma. A short straddle on expiry day is the highest-decay and highest-gamma position available simultaneously. There is no version that gives you one without the other.
Building strategies around expiry
Index option behaviour is not uniform across the week, so running the same strategy every day treats genuinely different conditions as identical.
Arthalab's builder lets you restrict a strategy to specific days, and the scheduler can auto-start live bots on chosen days relative to expiry. A strategy designed for expiry day should run on expiry day, not on every day because nobody switched it off.
1
Decide which part of the cycle the strategy is for
Expiry day, the day before, or the early part of a new series. These are different trades.
2
Restrict the days it runs
In the builder, so it does not trade conditions it was never designed for.
3
Size down for expiry day specifically
Higher gamma means the same position carries more risk than it does mid-week.
4
Set an exit time earlier than you think
The last thirty minutes near the strike offer little premium and considerable risk.
5
Backtest on expiry days alone
A sample mixing expiry and non-expiry days averages away the behaviour you are trying to measure.
Holidays and shifted expiries
When an expiry day falls on an exchange holiday, the expiry moves. This is announced in advance and is entirely routine, and it is also the most common cause of a strategy trading on a day its author did not intend.
A strategy keyed to a weekday will be wrong in any week where the expiry shifts. A strategy keyed to the expiry itself will not. This is one reason to express the schedule relative to expiry rather than to a day of the week.
The habit worth having
The exchange holiday calendar is published annually and revised occasionally. Checking it at the start of the year and again around major festival periods is a small habit that prevents a specific and avoidable surprise.
Liquidity on expiry day
Volume concentrates near the money as expiry approaches, and drains from strikes far away.
That is helpful if you are trading at the money and unhelpful if you need to exit a far strike. A position you could enter comfortably earlier in the week may be harder to close on expiry afternoon, precisely because everyone else has moved on from it.
Checking volume rather than open interest matters most on expiry day. High OI at a far strike with no volume means positions exist there and nobody is trading them.
The short version
- Decay accelerates and gamma rises — the attraction and the danger are the same mechanism
- Delta becomes nearly binary around the strike in the final hours
- Index options settle in cash, so there is no delivery obligation to avoid
- The settlement value is calculated by the exchange, not simply the last price
- Key a strategy to the expiry, not to a weekday, so holiday shifts do not break it
- Backtest expiry-day strategies on expiry days alone
For the current expiry schedule and holiday calendar, the exchange is the only reliable source. Any fixed answer in an article is correct only until the next revision.
Frequently asked questions
Time decay accelerates and gamma rises sharply at the money, while vega falls away. The result is a position that earns premium faster and can turn against you faster, from the same mechanism.
No. Index options in India settle in cash against the exchange's settlement value. There is nothing to deliver and no obligation to avoid by squaring off.
Not necessarily. The exchange calculates it using a defined method, which may differ from the final tick you watched.
Holding saves the exit cost and captures the last of the decay. Squaring off removes the risk of a late move through your strike. A defensible default is to close anything near the money and hold what is clearly out of it.
The expiry shifts, and the change is announced in advance. This is why a strategy should be keyed to the expiry rather than to a weekday — otherwise it trades the wrong day whenever the schedule moves.
Decay is fastest then, so a position held for a few hours captures a disproportionate share of the remaining premium. The same strikes also carry the most gamma, which is the cost of that attraction.
Generally no. Higher gamma means the same position carries more risk, so many traders reduce size specifically for expiry-day strategies.
NSE and BSE publish the contract specifications and the holiday calendar. Your broker's contract list also shows it. Schedules have been revised, so check the source rather than relying on an article.
Yes. The builder lets you restrict which days a strategy runs, and the scheduler can auto-start live bots on chosen days relative to expiry.
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