Options Expiry Week Dynamics
The options expiry week in Indian F&O — typically the last Thursday of the month for Nifty monthly contracts — was historically characterised by gamma expansion near at-the-money strikes, elevated intraday volatility, rising open interest concentration, and a volume surge as traders rolled or closed near-expiry positions.
As a Nifty monthly options contract approached its final settlement date, the mathematical properties of the options changed in ways that produced distinctive market behaviours. Gamma — the rate of change of delta with respect to underlying price movement — increased sharply for at-the-money and near-the-money strikes. In practical terms, this meant that small intraday moves in Nifty caused large changes in the delta of options sitting close to the money, resulting in rapid price swings in those options even for modest index moves.
For market makers and option sellers, elevated expiry-week gamma meant that delta hedging required more frequent rebalancing. Each intraday move needed to be offset by trading in the underlying futures or cash index, creating additional volume in futures and driving the round-trip hedging activity that was observable in NSE's daily turnover data. In expiry weeks, Nifty futures volume historically showed a meaningful elevation relative to non-expiry weeks.
Open interest patterns in expiry week reflected the 'pinning' behaviour around max pain levels. As the expiry date approached, open interest tended to concentrate at specific strikes — typically the at-the-money strike and one or two strikes on either side. This concentration meant that large movements beyond these strikes could trigger a cascade of delta hedging by entities with large short gamma exposure, amplifying moves in either direction before a reversal brought prices back toward the concentration zone.
Retail and proprietary traders also contributed to expiry-week volume surges through 'lottery' behaviour — purchasing deeply out-of-the-money options with small absolute premium (often 5-15 rupees per lot on Nifty) in the hope of a large move to expiry. While the probability of profit on such positions was low, the asymmetric payoff profile attracted speculative participation that temporarily distorted the implied volatility surface by inflating far out-of-the-money skew.
Theta decay was also at its most aggressive in expiry week. Options that were out-of-the-money with two or three days to expiry lost a significant portion of their remaining time value per day, making short-gamma strategies theoretically attractive while simultaneously exposing them to the elevated gamma risk.