Key Takeaways
- The Closing Auction Session (CAS) goes live today, August 3, 2026, for every NSE- and BSE-listed stock with active F&O contracts, replacing the old VWAP-based closing price method.
- Continuous trading for these stocks now ends at 3:15 PM instead of 3:30 PM, moving into a new 20-minute auction window.
- Equity derivatives trading is extended by 10 minutes to 3:40 PM, with a fresh post-close session from 3:50 PM to 4:00 PM.
- NSE ran its final mock rehearsal on Sunday, August 2, using NEAT+ version 7.8.9, per circular NSE/CMTR/75534 dated August 1, 2026.
- Non-F&O stocks are unaffected for now; a second phase covering the Pre-Open Auction Session follows on September 7, 2026.
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What Changes From Today
For stocks carrying active Futures & Options contracts, what exchanges call Category I securities, continuous trading now stops at 3:15 PM instead of 3:30 PM, moving straight into the Closing Auction Session. All other listed stocks, classified as Category II, continue trading until 3:30 PM as before, with their close still based on the 3:00-3:30 PM volume-weighted average.
On the derivatives side, NSE has extended trading hours for the equity derivatives segment by 10 minutes, moving the market close from 3:30 PM to 3:40 PM, covering index futures, index options, stock futures and stock options alike. A post-close session then begins 10 minutes after the derivatives segment shuts, keeping the closing-price sequence consistent across market segments.
Also Check: NSE Option Chain Live — Nifty, Bank Nifty & All F&O Stocks
The New CAS Timeline
| Phase | Time | What Happens |
|---|---|---|
| Continuous trading | 3:00 PM – 3:15 PM | Normal trading; VWAP of this window becomes the reference price |
| Transition | 3:15 PM – 3:20 PM | Continuous trading halts for CAS stocks; reference price and ±3% band locked |
| Order entry (open) | 3:20 PM – 3:25 PM | Market and limit orders accepted |
| Order entry (restricted) | 3:25 PM – 3:30 PM | Only limit orders allowed; market orders can’t be modified or cancelled |
| Random closure | 3:28 PM – 3:30 PM | System closes order entry at a random point |
| Matching | 3:30 PM – 3:35 PM | Orders matched; equilibrium price becomes the official close |
| Derivatives close | 3:40 PM | F&O trading ends |
| Post-close | 3:50 PM – 4:00 PM | Trades allowed at the official closing price |
Between 3:15 pm and 3:20 pm, the market transitions from the continuous trading session into CAS, with reference price calculation happening alongside; market and limit orders can then be placed between 3:20 pm and 3:25 pm, before the window narrows to limit orders only until 3:30 pm. Stock futures price bands are separately reset to a static ±3% based on their own 3:00 PM–3:15 PM VWAP at this point, with dynamic band flexing paused for the rest of the session.
NSE’s Final Rehearsal: Inside the August 1 Circular
The document behind this reform’s final dress rehearsal is NSE circular NSE/CMTR/75534 (Circular Ref. 109/2026), dated August 1, 2026, and signed by Associate Vice President Khushal Shah.
It called for a mock trading session on Sunday, August 2, one day before today’s live rollout, explicitly flagged as involving “no new version release,” meaning the terminal software itself was already finalised and this was purely a systems check.
Members trading through NEATPlus were told to run version 7.8.9, downloadable from /cmftp/common/NEATPlus789 on the NSE extranet, while the outgoing 7.8.8 build stays active in the mock environment through September 5.
The circular also listed the exact master files brokers needed loaded beforehand, security.gz, participant.gz, nnf_security.gz, nnf_participant.gz and the day’s NSE_CM_security file from the ntneat folder, plus cm_contract_stream_info.csv from tbt_masters.
It confirmed mock trades carry no fund pay-in or pay-out obligation, that only pre-approved UCC/PAN records could place orders, and that live re-login access was restored between 2:00 PM and 2:30 PM once the drill wrapped up.
Old VWAP Method vs New CAS Method
| Parameter | Old VWAP Method | New CAS Method |
|---|---|---|
| Basis | Average price of trades between 3:00-3:30 PM | Single equilibrium price from matched auction orders |
| Trading close (F&O stocks) | 3:30 PM | 3:15 PM, then a dedicated auction |
| Key risk | Large late orders could skew the average | Orders pooled into one book, limiting single-order impact |
| Coverage | Applied uniformly to all stocks | Applies only to Category I (F&O) stocks for now |
| Exchanges | NSE, BSE | NSE, BSE and MSEI |
Who Gets Impacted: Trader-Wise Breakdown
| Market Participant | Key Change | Action Point |
|---|---|---|
| Intraday/MIS traders | Square-off cutoffs on CAS stocks may move earlier, broker-dependent | Confirm your broker’s revised MIS cutoff before 3:15 PM |
| F&O traders | Derivatives trading now runs till 3:40 PM | Use the extra 10 minutes to react to the freshly discovered close |
| Mutual funds, index funds, ETFs | Large closing-day orders get pooled into one auction | Expect tighter NAV tracking against benchmark indices |
| Investors holding F&O-stock positions | Stop-loss orders on CAS-eligible stocks are not carried into the auction and get auto-cancelled | Recheck open stop-loss orders after 3:15 PM |
| Investors in non-F&O stocks | No change for now | Continue as usual under the existing VWAP method |
Since closing-price shifts often move alongside institutional positioning, tracking daily FII-DII activity on NiftyTrader’s FII-DII Tracker can help gauge how large players are adjusting to the new mechanism.
Why SEBI Pushed This Reform
SEBI introduced the CAS framework via circular HO/47/11/11(3)2025-MRD-POD2/I/2765/2026, dated January 16, 2026, following public consultations through discussion papers released on December 5, 2024 and August 22, 2025, along with deliberations by the Secondary Market Advisory Committee and feedback from exchanges, clearing corporations, mutual funds and foreign portfolio investors.
The regulator’s stated aim is to strengthen price discovery, pool market interest into a single liquidity pool, improve execution of large orders, and enhance transparency, given that the closing price feeds directly into derivatives settlement, index computation and mutual fund NAV calculation.
NSE then finalised the operating rules through its own implementation circular. A second phase, integrating the morning Pre-Open Auction Session into the same framework, is scheduled for September 7, 2026.
Bottom Line
CAS formally replaces VWAP for every NSE- and BSE-listed stock with live F&O contracts starting today, arriving a day after NSE’s last mock rehearsal confirmed the system was ready.
Traders in F&O-eligible stocks now work with a shorter continuous session and a fresh 20-minute auction window, while investors in non-F&O names see no change yet. The real test begins with today’s 3:15 PM close.
Read Next: Stocks in Focus August 3: Maruti, ITC, ZEE, Persistent in Focus Ahead of RBI Policy and Q1 Earnings
This article is for informational purposes only and does not constitute investment advice. Investors are advised to verify exchange circulars directly on nseindia.com and consult SEBI-registered advisors before making trading decisions
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