Expiry Day Option Selling: Mechanics, Risk and Position Management

Expiry day concentrates option selling’s best and worst characteristics into a few hours. Time value collapses fastest, which is what attracts sellers, and gamma is at its most extreme, which is what removes accounts. Both facts come from the same source: there is almost no time left.

Why sellers are drawn to expiry

Theta decay accelerates as expiry approaches, and on the final day the remaining time value in an out-of-the-money option decays to zero within hours. A seller collecting that premium is capturing decay at its fastest rate.

The attraction is real. The problem is that the same compression of time produces the risk.

Gamma is the actual danger

Gamma measures how quickly delta changes. Near expiry with the underlying close to the strike, an option’s delta can swing from near zero to near one on a modest move — meaning a position that was effectively flat becomes fully directional almost instantly.

For a short option this is the worst possible behaviour: losses accelerate exactly when you have least time to recover. A strike that looked comfortably out of the money at midday can be deep in the money by close, and there is no time value left to cushion it.

This is why expiry-day option selling produces outsized losses relative to the premium collected. The premium is small because time is short; the risk is large for the same reason.

Managing it if you do it

• Define the risk structurally. Sell spreads rather than naked options — the long leg caps the worst case that gamma can produce.
• Size well below normal. Expiry positions are not comparable to ordinary short-premium trades.
• Set the exit before entry. Deciding mid-move, when delta is swinging, is where discipline fails.
• Respect strike proximity. Risk rises non-linearly as the underlying approaches your strike.
• Watch margin. Requirements on short options near the money at expiry rise sharply, precisely when you are under pressure.

Stock options: the settlement trap

Index options settle in cash. Stock options settle physically — an in-the-money short stock option carried to settlement creates a delivery obligation for the full lot value. Traders have discovered obligations of several lakh rupees on positions that collected a few thousand in premium.

Know your contract’s settlement type before the final session. This is a rule, not a matter of judgement.