SEBI Overhauls Closing Auction Rules, Alters Expiry Settlement Pricing From December 7 Market regulator SEBI has amended the Closing Auction Session mechanism, modifying how derivative settlement prices are calculated on expiry days and scheduling implementation from December 7. Shares of India's leading stock exchanges witnessed notable selling pressure during Friday's session on October 16, following the release of an extensive circular by the Securities and Exchange Board of India. The market regulator issued the directive late Thursday evening, outlining substantial modifications to the operational framework governing the Closing Auction Session. These regulatory changes alter the mechanics of derivative expiry settlements across trading venues, while setting up explicit procedural timelines for market closing sessions and the migration of institutional order flow. Exchange Stocks Retreat Following Circular The market reacted immediately to the regulator's late-night circular during trade on Friday. Shares of Bombay Stock Exchange declined by 1.82 percent during the session. At the time of evaluation, the BSE counter was trading lower at Rs 3,370.80. Concurrently, shares of the National Stock Exchange of India also experienced downward movement, sliding 0.50 percent to trade at Rs 1,765. The NSE counter subsequently traded lower, reaching Rs 1,761 per share as market participants processed the operational ramifications of the revised clearing and settlement mechanisms. Revised Methodology for Derivative Expiry Settlements Among the critical revisions introduced in the framework is the procedure for computing the final settlement price for both index and single stock derivative contracts on their respective expiry days. Under the updated regulatory requirements, the settlement price for index derivatives will now be derived directly from the underlying index valuation. This valuation will be established using the Volume Weighted Average Price of its constituent equities during the final 30 minutes of the Continuous Trading Session. This methodology represents a distinct departure from the earlier closing auction architecture, which had contemplated utilizing auction-determined closing prices to compute final derivative settlements on expiry days. The revised structure will also apply uniformly to individual stock derivative contracts on their expiration sessions and will be mandated across all operational domestic equity exchanges. Industry participants observe that anchoring the expiry settlement to the 30-minute continuous trading VWAP helps mitigate price distortions and volatility surges that often materialize during concentrated auction windows. Structure and Timeline of the Ten-Minute Closing Auction The regulator has formally delineated a structured 10-minute Closing Auction Session window operating between 3:30 PM and 3:40 PM. This post-continuous trading block will feature specific sub-windows dedicated to system transitions, quote collection, and price finalization. The regulatory schedule specifies the following timeline • 3:30 PM to 3:31 PM: A one-minute transition window allocated for system shifts and establishing the reference baseline price. • 3:31 PM to 3:36 PM: A five-minute trading phase permitting market participants to input both limit orders and market orders. • 3:36 PM to 3:40 PM: A four-minute phase where entry is strictly restricted to limit orders, prohibiting any new market orders. • 3:38 PM to 3:40 PM: A final overlapping two-minute interval designated for the algorithmic determination and finalization of closing prices. The reference benchmark price utilized throughout this closing auction will be calculated using the Volume Weighted Average Price of all continuous trades executed during the final 15 minutes of the standard continuous trading session. This baseline provides an anchored range for order matching during the subsequent auction. Treatment of Unexecuted Iceberg Orders Clarified The circular also provides precise clarity regarding the status of pending iceberg orders once the standard continuous trading session concludes. Iceberg orders represent massive trade volumes that institutional desks divide into automated, smaller limit tranches to prevent disclosing the comprehensive order size on the public order book. Under the revised directive, any iceberg orders that remain unfilled at the conclusion of continuous trading will automatically roll over into the Closing Auction Session as standard, fully disclosed limit orders, provided the trader has not cancelled them. Regarding execution sequencing, the regulator established a tiered time priority standard. These carried-over orders will hold lower execution priority compared to standard limit orders originally placed during the Continuous Trading Session. However, they will retain higher priority than entirely new orders submitted during the Closing Auction Session itself, preserving queue equity across participants. Staggered Implementation Schedule The regulatory framework sets a two-tier timeline for market implementation. The majority of the revised provisions, including the updated 30-minute VWAP expiry settlement calculation and the closing auction schedule, will take effect on December 7. Meanwhile, the specialized technical infrastructure required to manage the migration and disclosure of unexecuted iceberg orders into the closing auction will follow an extended transition period, taking effect later on February 8, 2027. What this means for you SEBI's amended closing mechanism will directly alter trade management, execution timing, and margin risks for derivative market participants and institutional desks. • Derivative Traders: Contract settlements on expiry days will depend on the final 30-minute continuous VWAP rather than auction prints, curbing artificial price spikes. Traders must adjust their roll-over and square-off timings ahead of the December 7 deadline. • Closing Auction Execution: Market orders will only be valid from 3:31 PM to 3:36 PM, after which the book allows only limit orders until 3:40 PM. Participants must adapt order routing setups to prevent execution rejections during the final minutes. • Institutional Iceberg Orders: Unfilled hidden tranches will convert to fully disclosed limit orders in the closing auction, altering liquidity dynamics. Market participants have until February 8, 2027, before this specific routing becomes mandatory across trading desks. • Exchange Stock Investors: Both BSE and NSE shares experienced price drops following the circular due to technical adjustments. Equity investors in exchange platforms should monitor trading volumes under the new framework. Why this happened SEBI introduced these operational revisions to eliminate end-of-day price manipulation risks on expiry sessions and provide structural predictability to market closings. The regulator reshaped earlier proposals following technical assessments regarding auction volatility and settlement reliability. • Mitigating Expiry Volatility: Relying purely on closing auction prints for derivative expiries made indices vulnerable to targeted distortion by large market orders. Shifting settlement calculation to a 30-minute continuous VWAP distributes pricing volume across a broader operational timeframe. • Enhancing Transparency for Large Trades: Transitioning unexecuted iceberg tranches into fully visible limit orders prevents hidden liquidity imbalances during price-matching auctions. This guarantees that all auction participants compete with accurate visibility of open interest and depth. • Structured Auction Flow: Dividing the 10-minute session into distinct intervals for order entry and price matching prevents technical bottlenecks. Restricting the final four minutes exclusively to limit orders avoids chaotic last-second price whipsaws. Questions & Answers 1. When do SEBI's new Closing Auction Session rules take effect? Most provisions will come into force on December 7, while the rules for unexecuted iceberg orders become effective on February 8, 2027. 2. How will derivative settlement prices be calculated on expiry days? Settlement prices will be calculated using the Volume Weighted Average Price (VWAP) of constituent stocks during the final 30 minutes of the Continuous Trading Session. 3. What is the duration and timing of the Closing Auction Session? The dedicated session will run for 10 minutes, starting at 3:30 PM and ending at 3:40 PM. 4. Until what time can market orders be placed during the closing auction? Market orders are accepted only between 3:31 PM and 3:36 PM, after which only limit orders are permitted until 3:40 PM. 5. What happens to unexecuted iceberg orders when regular trading closes? Unless cancelled, they are rolled into the Closing Auction Session as fully disclosed limit orders with tiered priority. 6. How did exchange shares react to SEBI's circular? On Friday, October 16, BSE shares fell 1.82 percent to Rs 3,370.80, while NSE shares fell 0.50 percent to Rs 1,765. https://trendkia.com/en/money/sebi-ne-badala-closing-auction-session-ka-dhancha-expiry-settlement-ke-nae-niyama-7-disnbara-se-honge-lagu-48397 TrendKia — Har trend, sabse pehle.