SEBI Closing Auction Session VWAP: What It Means for Open Offer and Buyback Pricing

Updated 18 October 2026 after SEBI's final circular. An earlier version of this article treated the settlement-price options in the consultation as inputs to ICDR and Takeover Code VWAP floors and suggested dual-track workpapers. They weren't inputs, and the analysis below has been corrected.

SEBI has issued its final circular on the Closing Auction Session (CAS). The circular of 15 October 2026 settles expiring index and stock derivatives on the VWAP of the last 30 minutes of continuous trading, moves the auction to 3:30-3:40 pm, and applies from 7 December 2026, with the iceberg-order provisions following on 8 February 2027.

For a pricing committee the useful reading is about scope. The circular amends the January 2026 CAS framework and Chapter 5 of the Master Circular for Stock Exchanges and Clearing Corporations (para 4). It doesn't amend the ICDR, SAST, Delisting, Buy-back or SBEB Regulations. So the question isn't which settlement method your merchant banker will use. It's which of your pricing formulas use the closing price, and which use a multi-day average of the day's trades.

The session changes are covered in detail in the companion piece on what changes on 7 December 2026. This one deals with regulatory pricing.

What SEBI decided

SEBI introduced CAS in the equity cash segment through a circular dated 16 January 2026. From 3 August 2026, stocks with derivatives contracts began closing on an auction price instead of the VWAP of trades in the last 30 minutes of continuous trading, and that auction close became the basis for expiry-day settlement of derivatives. Stocks without derivatives kept the 30-minute VWAP close (para 4.1 of that circular).

The September 2026 consultation offered two ways to settle derivatives: a blended VWAP of the last 30 minutes of continuous trading plus the auction, or an interim CTS-only VWAP. It drew more than 20,000 responses, most favouring the CTS-only route, Business Standard reported.

The final circular adopts CTS-only settlement with no stated move to a blend later. Under para 4.9.1, expiring index derivatives settle on an index value computed from the constituents' VWAPs in the last 30 minutes of continuous trading, and expiring stock derivatives settle on the stock's VWAP in that window across all exchanges. The auction runs from 3:30 to 3:40 pm with a random close between 3:38 and 3:40 pm (paras 4.2.1 and 4.2.2), and the closing price for stocks with derivatives is still the one discovered in the auction (para 4.2.3).

Why the settlement decision doesn't reach your pricing floor

The settlement price is a number the clearing corporations compute to close out expiring futures and options. The pricing floors in SEBI's issuer regulations draw on something else.

ICDR Regulation 164(1) sets the floor for a preferential issue of frequently traded shares at the higher of the 90-trading-day VWAP and the 10-trading-day VWAP of the shares quoted on the recognised stock exchange preceding the relevant date. The exchange is the one with the highest trading volume in the preceding 90 trading days. The SAST Regulations include, for frequently traded shares, the volume-weighted average market price for the 60 trading days before the public announcement (Regulation 8(2)(d)), and define that price as the product of shares traded on a stock exchange and their price, divided by total shares traded (Regulation 2(1)(zb)). The Delisting Regulations use the same 60-trading-day measure for the floor price (Regulation 19A(1)(iv)).

None of these refers to the closing price, the last 30 minutes of trading or the derivatives settlement price. They average the day's trades on the exchange over 10, 60 or 90 trading days. The CTS-only versus blended debate was never about their inputs, and the October circular doesn't touch their text.

Where the closing auction still matters

Some formulas do use the closing price, and for a stock with derivatives that price has come from the auction since 3 August 2026. The October circular keeps it that way, only later in the day.

The new wrinkle for these closing-price rows is expiry day. From 7 December the derivatives settlement price and the cash-segment closing price of an F&O stock will be different numbers on every expiry day. A floor computed from the wrong one would be wrong. The Buy-back Regulations and the SBEB Regulations refer to the closing price on a stock exchange, which is the cash segment, so the source has to be the exchange's published close.

The question the circular leaves open

The VWAP and volume-weighted average market price definitions don't carve out any trading session. On a plain reading, trades executed in the closing auction and in the 3:50-4:00 pm post-close session are trades on the exchange like any other. The circular doesn't address the point, and this review hasn't found exchange guidance on whether the daily VWAP series used for regulatory pricing includes those trades.

It matters more than the settlement debate did. A 90-trading-day window ending in October 2026 already straddles 3 August, when auction trades first appeared for F&O stocks. From 7 December the mix shifts again, because continuous trading in those stocks runs to 3:30 pm and the auction shrinks to 10 minutes. If auction volume is in the series, its share of each day's volume changes with the timetable. If it isn't, the series excludes a slice of real trading. Either way, the merchant banker's certificate should say which data series it used.

Timeline

• 16 January 2026: SEBI circular introduces CAS for stocks with derivatives.
• 3 August 2026: CAS goes live, 3:15 to 3:35 pm, with derivatives settling on the auction close.
• 3 September 2026: SEBI announces a review of the settlement-price methodology.
• 12 September 2026: Consultation paper proposes blended or CTS-only VWAP settlement.
• 3 October 2026: Comment window closes.
• 15 October 2026: Final circular adopts CTS-only settlement and moves CAS to 3:30-3:40 pm. Exchanges and clearing corporations have seven days to revise their procedures (para 5).
• 7 December 2026: Most changes take effect (para 6.1).
• 8 February 2027: Rules on carried-forward and iceberg orders in para 4.8 take effect (para 6.2).

The same habit of tracking effective dates, not announcement dates, applies to the items cleared at SEBI's 24 September 2026 board meeting.

What pricing committees should do for Q3 and Q4 FY27

Drop the dual-track workpapers. Parallel computations under CTS-only and blended methods made sense only if the settlement method fed the floor, and it doesn't. Any preferential issue, open offer or delisting with a relevant date, public announcement date or reference date in Q3 or Q4 FY27 runs on the same formula as before.

Ask for a data-source note instead. The merchant banker should confirm which exchange's series was used, why that exchange qualifies under the relevant regulation, and whether the daily VWAP includes auction and post-close trades. That note covers both the 3 August and 7 December changes in one paragraph.

Mark the session dates in the workpaper. For a window that crosses 3 August 2026, 7 December 2026 or both, record which session timings applied to each date. That costs little and answers the first question an auditor or regulator is likely to ask.

Check every closing-price input on expiry days. For QIPs, book-built buy-backs and SBEB computations involving an F&O stock, confirm that the closing price came from cash-segment data, especially where the relevant date or notice date falls on a derivatives expiry.

Keep disclosure language accurate. Explanatory statements and letters of offer don't need warnings about a pending methodology change any more, since the review is closed. A single line naming the data source is enough.