The Securities and Exchange Board of India (SEBI) is planning to reverse its recently implemented mechanism for determining final derivatives settlement prices, considering a move to decouple derivative expirations from the newly rolled-out Closing Auction Session (CAS). According to reports from market participants and regulatory sources on October 5, 2026, the capital markets regulator is preparing to reinstate the traditional 30-minute Volume-Weighted Average Price (VWAP) of the continuous trading session (CTS) to settle equity futures and options contracts for a period of at least one year.
The proposed policy adjustment follows significant volatility, erratic price spikes, and operational friction observed on weekly and monthly index expiry days. After receiving approximately 20,000 public and institutional responses to its September consultation paper on closing mechanics and market timings, SEBI is leaning toward keeping the discrete auction mechanism strictly for establishing official cash-market stock closing prices, while shielding expiring derivatives contracts from auction-driven settlement swings.
Key Takeaways
- Settlement Decoupling: SEBI is likely to halt the use of the Closing Auction Session for calculating derivatives expiry settlement prices for at least one year.
- Return to 30-Minute VWAP: Final settlement prices for index and stock derivatives will instead be computed using the volume-weighted average price (VWAP) of executed trades during the last 30 minutes of continuous trading (3:00 PM to 3:30 PM).
- Cash Market Auction Retained: The Closing Auction Session (CAS) will remain active to determine the official end-of-day closing prices for cash equities, ETF unit calculations, and mutual fund Net Asset Values (NAVs).
- Public Pushback Response: The reversal comes after SEBI received roughly 20,000 submissions responding to its mid-September consultation paper, which had proposed alternatives including a “Blended VWAP” model.
- Implementation Horizon: Formal circulars and exchange-level testing protocols are expected by late October 2026, ahead of the next major monthly derivatives contract expiry.
THE PROPOSED DERIVATIVES SETTLEMENT TRANSITION
AUGUST 2026 FRAMEWORK (Closing Auction Session):
┌─────────────────────────┐
│ Continuous Trades End │ ──► 20-Minute Discrete Auction Book ──► Single Clearing Price
│ (Cut off at 3:15 PM) │ (3:15 PM – 3:35 PM) • Sets Cash Close
└─────────────────────────┘ • Settles Expiring F&O
(High Expiry-Day Volatility)
PROPOSED AMENDMENT (Decoupled Dual-Track Mechanism):
┌────────────────────────────────────────────────────────────────────────┐
│ CONTINUOUS TRADING (3:00 PM – 3:30 PM) │
└───────────────────┬────────────────────────────────┬───────────────────┘
│ │
▼ ▼
[ DERIVATIVES SETTLEMENT TRACK ] [ CASH EQUITIES CLOSING TRACK ]
• 30-Minute CTS VWAP Calculated • Eligible shares enter CAS (Auction)
• Dilutes late-order spikes • Discovers equilibrium cash price
• Used strictly for final F&O P&L • Used for NAVs, Indices & ETFs
• PAUSES CAS IN DERIVATIVES • Retained for cash market stability
The Operational Trigger: Why the Closing Auction Caused Friction
In August 2026, SEBI introduced the Closing Auction Session (CAS) for securities with available Futures and Options (F&O) contracts. Operating between 3:15 PM and 3:35 PM, the mechanism was designed to align Indian equity bourses with global exchanges (such as the NYSE and London Stock Exchange) by replacing trade-averaged closing calculations with a single multilateral order-matching auction at an equilibrium price.
However, while call-auction mechanisms function smoothly for passive portfolio index balancing, coupling the auction directly to derivatives expiry settlement created unexpected market distortion:
- Order Concentration & Thin Auction Books: Unlike continuous trading, where volume is absorbed continuously, call auctions aggregate orders and match them in a single clearing event. On expiry days, aggressive hedging, dynamic option delta-adjustments, and automated algorithmic orders were concentrated into the auction window, causing sharp price divergence from the preceding trading day.
- “Cliff-Edge” Settlement P&L: Because cash-settled index options (such as Nifty 50 and Bank Nifty) carry heavy open interest, a fractional tick in the final settlement price determines whether thousands of out-of-the-money (OTM) options expire worthless or finish in-the-money (ITM). Late-auction order shifts led to wild settlement swings, frustrating retail and institutional market participants.
- Surge in Late Derivative Turnover: Average derivative traded value per minute spiked dramatically near market close. On the National Stock Exchange (NSE), average per-minute derivatives turnover during the 3:20 PM to 3:30 PM window surged to ₹189.82 crore under CAS (up from ₹126.31 crore prior to the rollout). On the BSE, per-minute volumes doubled from ₹141.48 crore to ₹288.94 crore, illustrating severe order clustering.
The Mechanism: 30-Minute VWAP vs. Blended Calculation
In mid-September 2026, SEBI issued a formal discussion paper outlining two structural alternatives to address expiry-day distortions:
| Mechanism Dimension | Option 1: Blended VWAP | Option 2: 30-Minute CTS VWAP (Favored) |
| Data Inputs | Weighted blend of trades during continuous trading (3:00–3:15 PM) + trades matched in CAS (3:15–3:35 PM). | Trades executed strictly during the final 30 minutes of continuous trading (3:00 PM to 3:30 PM). |
| Auction Involvement | Partially dependent on closing auction liquidity. | Completely decoupled from the closing auction. |
| Complexity & Latency | High computational complexity; requires complex cross-exchange normalization formulas. | Familiar, battle-tested methodology previously used across Indian bourses for over a decade. |
| Market Feedback | Concerns over opacity and delayed calculation on fast expiry closes. | Supported by majority of 20,000 public and broker submissions. |
| Proposed Duration | Proposed as a permanent hybrid model. | Temporary 1-year interim pause on CAS for derivatives while monitoring market structure. |
Under the 30-minute VWAP system, the settlement price is calculated by taking the aggregate traded value of all transactions in a contract’s underlying equity or index components between 3:00 PM and 3:30 PM, divided by the total volume traded in that window:
$$\text{VWAP} = \frac{\sum (\text{Price}_i \times \text{Volume}_i)}{\sum \text{Volume}_i}$$
Because the calculation averages thousands of discrete executions over 1,800 seconds, the capital outlay required for an algorithmic trader or large entity to manipulate the final settlement price increases significantly, smoothing out the price spikes that occurred during the closing auction sessions.
Impact on Brokers, Algo Desks, and Retail Traders
Reverting derivatives settlement to the 30-minute continuous VWAP while retaining the closing auction for cash equities establishes a dual-track operational framework:
┌────────────────────────────────────────────────────────────────────────┐
│ MARKET PARTICIPANT IMPACT MATRIX │
├──────────────────┬─────────────────────────────────────────────────────┤
│ TRADER SEGMENT │ OPERATIONAL & RISK IMPLICATIONS │
├──────────────────┼─────────────────────────────────────────────────────┤
│ Retail Option │ • Reduced risk of unexpected ITM/OTM flip at close. │
│ Buyers & Sellers │ • Lower margin call volatility on expiry evenings. │
├──────────────────┼─────────────────────────────────────────────────────┤
│ High-Frequency & │ • Algos must recalibrate execution schedules from │
│ Algo Desks │ discrete auction matching back to time-slicing │
│ │ TWAP/VWAP algorithms over 3:00–3:30 PM. │
├──────────────────┼─────────────────────────────────────────────────────┤
│ Broker Risk │ • Earlier visibility into settlement baselines; │
│ Management Desks │ fewer post-market margin shortfall penalties. │
├──────────────────┼─────────────────────────────────────────────────────┤
│ Mutual Funds & │ • Continue using CAS for equity block tracking, │
│ Index Funds │ passive index rebalancing, and NAV computation. │
└──────────────────┴─────────────────────────────────────────────────────┘
For retail options participants—who comprise a significant portion of daily index volume—the move reduces the risk of unanticipated physical delivery or exercise assignments.
Under CAS settlement, an index or underlying stock hovering near a strike price at 3:14 PM could be pushed into the money by the 3:35 PM auction matching, triggering higher margin requirements or delivery liabilities before broker risk engines could react.
What Remains Uncertain
While regulatory momentum favors the 30-minute VWAP reinstatement, several technical details remain to be finalized:
- Market Timings Alignment: If cash-market continuous trading ends at 3:30 PM, but equity derivatives trade until 3:40 PM or later, exchanges must ensure that underlying spot VWAP calculation feeds are broadcast to derivatives clearing systems in real time.
- Handling Illiquid Single-Stock F&O: For thinly traded mid-cap equities with active F&O contracts, if trading volume in the final 30 minutes is low, the resulting VWAP calculation can be skewed by small odd-lot trades. SEBI must specify whether fallback rules (such as using the last traded price or expanding the window) will apply.
- The 1-Year Review Horizon: The pause on CAS for derivatives is framed as a temporary, one-year measure. Regulators will monitor whether exchanges can refine the auction book’s order-masking and depth parameters during this period before reconsidering whether to integrate derivatives back into the closing auction.
What Happens Next
SEBI’s Secondary Market Advisory Committee (SMAC) is expected to review the public consultation findings and deliver its final recommendations to the SEBI Board before mid-October 2026:
- Formal Exchange Directives: The National Stock Exchange (NSE) and BSE will issue operational circulars detailing the cut-off times for continuous trade inputs and derivatives settlement timestamps.
- Algorithm Certifications: Trading algorithm vendors and institutional brokerages will update and re-test their execution algorithms to ensure order-routing engines align with the continuous VWAP calculation window.
- Go-Live Target: The regulator is targeting the formal deployment of the revised settlement rules before the end of October 2026.
Frequently Asked Questions
Why is SEBI considering moving derivatives settlement back to a 30-minute VWAP?
SEBI is considering the move due to sharp price volatility and erratic swings observed on expiry days under the recently introduced Closing Auction Session (CAS). Shifting back to a 30-minute continuous VWAP averages trade execution across thousands of transactions, smoothing out abrupt settlement spikes.
Will the Closing Auction Session be completely eliminated?
No. The closing auction is expected to remain in place for cash equities to discover the official closing price of underlying stocks, calculate index values, and determine mutual fund Net Asset Values (NAVs). Only the calculation for derivatives expiry settlement will be decoupled from the auction.
What was the proposed “Blended VWAP” alternative?
The Blended VWAP proposal was a hybrid calculation that combined trades executed during the last 30 minutes of continuous trading with the orders matched during the Closing Auction Session. However, market participants favored returning to the simpler, proven 30-minute continuous trading VWAP.
When are these changes expected to take effect?
SEBI is targeting the implementation of the revised derivatives settlement rules by the end of October 2026, following formal circulars and technical testing across stock exchanges.
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