Expiry day once followed a familiar rhythm. Traders watched the final 30 minutes, calculated the likely closing price using VWAP, and used short-term movements to scalp option premiums. Many strategies were built around the belief that the market would behave as it had before. That belief now needs to be tested.
From August 3, eligible F&O stocks began using a Closing Auction Session, or CAS, to determine the closing price. Cash-market trading ends at 3:15 pm, the auction runs from 3:15 pm to 3:35 pm, and derivatives trading continues until 3:40 pm. The closing price is discovered through an auction equilibrium instead of the earlier VWAP-based method.
For traders who continue using old expiry strategies without checking whether they still work, the market may become an expensive teacher.
The first adaptation is to stop trading with outdated assumptions.
Earlier, traders could calculate the VWAP during the final 30 minutes and compare the market price with that average. If the price moved too far from the estimated closing level, they attempted to scalp the difference. The method was not risk-free, but it gave traders a familiar reference point.
The new auction process changes that reference. Strategies designed for the old market have therefore lost their advantage.
The sensible response is patience. Traders should observe at least four expiry sessions under the new system before deciding which strategy to use. They should record price movements, option premiums, Open Interest changes, and auction-period behavior. They should also compare actual auction outcomes with earlier estimates, noting where price, liquidity, and option premiums behaved differently.
This observation period can reveal whether it is possible to build a genuine strategy around the new market structure. Traders should resist the temptation to draw immediate conclusions after one successful or unsuccessful expiry.
The second adaptation is to reduce blind scalping. Fast premium movements can create excitement, but excitement is not an edge. Traders should enter only when price action is supported by derivatives data, including Open Interest and Futures Build-up.
The third adaptation is to prefer defined-risk strategies. Iron Flies and Iron Condors may suit range-bound conditions, while spreads can limit losses when traders have a directional view. Position sizes should also be smaller because sudden order flow can reverse a favorable trade.
Market structure changes, and trading methods must change with it. The new expiry mechanism does not mean opportunities have disappeared. It means familiar signals need to be tested again.
Professional traders will watch before acting. They will study the new auction process, avoid emotional scalping, use derivatives data, and define their maximum loss. Most importantly, they will accept that staying out of a trade is sometimes the better decision.
On expiry day, patience is not hesitation. It is preparation. Traders who wait for reliable evidence give themselves a better chance of protecting capital and finding an edge in the market’s new rhythm.
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