A ₹1 lakh Sensex options position could theoretically have produced about ₹44 lakh in profit during the violent market swing on F&O expiry day. This was not a confirmed account of every trader making money. It was a social-media example based on buying the Sensex 76,500 put option before the index plunged and selling it after the option premium multiplied.
The event attracted attention because it happened around India’s new Closing Auction Session, or CAS. The Sensex reportedly fell more than 2,200 points within about five minutes and then recovered nearly 2,000 points before the closing price was finalised. Such a rapid move can make near-expiry option prices rise or collapse at extraordinary speed.
What is CAS in the stock market?
CAS stands for Closing Auction Session. It is a separate auction used to determine the official closing price of eligible shares in the equity cash market. SEBI introduced the framework to make closing-price discovery more transparent and align India with auction systems used by several major global exchanges.
CAS does not mean that everyone trades continuously at the temporary prices displayed during the auction. Buyers and sellers submit orders, and the exchange calculates one equilibrium price at which the maximum possible quantity can be matched.
What time does the Closing Auction Session operate?
According to NSE’s CAS framework, the session runs from 3:15 pm to 3:35 pm on trading days.
- 3:15 pm to 3:20 pm: The exchange calculates the reference price and shifts from continuous trading to CAS.
- 3:20 pm onward: Eligible limit and market orders enter the auction process.
- Final part of order collection: Only limit orders are permitted, with a system-driven random closure near the end.
- Up to 3:35 pm: Orders are matched and trades are confirmed at the equilibrium price.
The reference price is based on the volume-weighted average price of trades executed between 3:00 pm and 3:15 pm. During CAS, the permitted band is generally 3% above or below that reference price for eligible shares.
Which shares come under CAS?
In the first phase, CAS applies to cash-market stocks on which derivative contracts are available. These include many large and actively traded companies that influence the Nifty and Sensex. Stocks outside the initial CAS list continue to use the earlier closing-price method.
The auction affects index movements because the Sensex and Nifty are calculated from the prices of their constituent shares. If heavily weighted stocks such as Reliance Industries or major banks show sharp indicative price changes, the displayed index can swing significantly.
What happened to the Sensex on F&O expiry day?
During the first monthly BSE derivatives expiry after CAS began, the Sensex and Bankex showed unusually large movements near the close. The Sensex reportedly dropped more than 2,200 points between approximately 3:18 pm and 3:23 pm. It then recovered almost 2,000 points by around 3:30 pm and finally closed at 76,934, down 539 points from the previous close.
Some heavyweight Sensex shares also displayed rapid changes. Reliance Industries reportedly moved from about ₹1,289 to ₹1,250, a fall close to the 3% CAS band, before recovering toward ₹1,286.
How could ₹1 lakh become ₹45 lakh?
The widely shared example involved the Sensex 76,500 put option. A put option generally gains value when its underlying index falls, especially when the fall is sudden and the contract is close to expiry.
Suppose a trader bought put options worth ₹1 lakh before the sharp decline. As the Sensex crashed, the probability of the index finishing below the strike price increased quickly. The option premium could therefore jump many times within minutes.
If the total position value rose from ₹1 lakh to approximately ₹45 lakh, the calculation would be:
- Initial option value: ₹1,00,000
- Exit value: approximately ₹45,00,000
- Gross profit: approximately ₹44,00,000
- Value multiplication: about 45 times
This is why the report referred to a ₹44 lakh profit from ₹1 lakh. The final position value would be about ₹45 lakh. Brokerage, taxes, slippage and execution differences would reduce the actual net profit.
Was the ₹44 lakh profit a verified trade?
No verified contract note or exchange-confirmed trader record was cited for the ₹44 lakh figure. The number came from a trader’s social-media observation describing what could have happened if someone bought the option near 3:15 pm and exited around 3:20 pm.
It should therefore be treated as a theoretical or chart-based opportunity, not proof that a known trader successfully entered and exited the entire position at those exact prices.
Why did the option price rise so sharply?
Three forces likely combined. First, the Sensex moved thousands of points in a very short period. Second, it was expiry day, when option premiums are extremely sensitive to the index’s distance from the strike price. Third, limited time and fast-changing liquidity can produce wide differences between the displayed price and the price at which a large order can actually execute.
A near-expiry option can move from almost worthless to valuable if the index suddenly crosses or approaches its strike. The reverse is also true. When the Sensex recovered, the same put option could have lost most of its inflated value within minutes.
Did traders make the money inside CAS?
Not directly in the cash-market auction. CAS determines the closing prices of eligible shares. Sensex options trade in the derivatives segment, which remains open beyond the cash auction window. The violent indicative movements in constituent shares and the index affected the value of derivatives linked to the Sensex.
In simple terms, the cash-market auction created or reflected a sharp index movement. Options traders attempted to profit from the resulting change in the Sensex options premium.
Could a trader also lose the full ₹1 lakh?
Yes. A buyer who entered after the option premium had already surged could have suffered a rapid loss when the Sensex recovered. If the option expired out of the money, the premium could fall close to zero. The trader could lose almost the entire ₹1 lakh.
Execution was another major risk. A price visible on a screen does not guarantee that every order could be filled at that level. Fast markets can have thin liquidity, rejected orders, slippage and sudden bid-ask changes. A theoretical chart profit can be very different from money actually realised.
Why was CAS introduced?
Before CAS, India generally calculated closing prices using the volume-weighted average price during the final part of regular trading. SEBI introduced the closing auction to gather buy and sell interest at one time and calculate a single equilibrium price.
The goal is to improve closing-price discovery, provide equal access to investors and reduce disruption from large institutional orders. However, the expiry-day episode has raised questions among traders about indicative index volatility, coordination between cash and derivatives closing mechanisms and the behaviour of heavily weighted stocks.
CAS and ₹44 lakh profit FAQs
What is the full form of CAS?
CAS means Closing Auction Session. It is used to determine the official closing price of eligible cash-market stocks.
Did ₹1 lakh become ₹44 lakh?
The claim means a ₹1 lakh options position could have reached about ₹45 lakh, creating roughly ₹44 lakh gross profit. It was a theoretical example, not a verified universal result.
Did the profit happen in one minute?
The cited example covered roughly five minutes, from around 3:15 pm to 3:20 pm. Prices may have changed sharply within individual minutes, but the reported calculation was not a one-minute confirmed trade.
Is CAS available for all stocks?
No. In the first phase, it applies to cash-market stocks that have derivative contracts.
Can traders repeat this profit?
There is no reliable way to repeat such an exceptional move. Options can lose their value just as quickly. This event should not be treated as a trading strategy or guaranteed return.
This article explains a reported market event and is not investment advice. Options trading carries a high risk of rapid and total loss.