Closing Auction Session
The 15:15 freeze, the auction print vs futures-implied cash, expiry-day settlement risk and the print-reversion history — NIFTY to SENSEX, every session on both exchanges since the CAS went live.
What this page tracks
Since 3 August 2026 the official NSE and BSE closing price is set by a Closing Auction Session (CAS) — both exchanges launched the same day: continuous trading in the underlying stocks ends at 15:15, a call auction collects orders while the index feed stays frozen, and the auction equilibrium becomes the official close in a single reprint at around 15:28–15:30. F&O keeps trading against that print until 15:40. This page tracks each session's freeze level, the auction print, whether the derivatives market accepts it, and what it does to option settlement on expiry days — live through the close window, and replayable for any past session — for NIFTY, SENSEX, BANKNIFTY, BANKEX and the other tracked indices via the index switcher.
Watch the tutorial
Closing Auction, section by section, in a 3-minute video, also in Hindi, Tamil, Telugu, Kannada and Malayalam.
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How to read it
- Freeze level — the index value held from 15:15 while auction orders are collected. Every normal app shows this frozen number — it is not the closing price.
- Auction print — the equilibrium price that becomes the official close. It can land far from the frozen tape; the first CAS session printed +200.95 pts above it, outside the day's entire traded range.
- Futures-implied cash — the futures price minus the pre-freeze basis — where the derivatives market says the index should be. A large gap between the print and this number means the official close and the traded market disagree.
- Settlement monitor (expiry days) — weekly option settlement equals the official close, i.e. the auction print. While the tape is frozen, expiring option prices leak the auction equilibrium (at settlement C − P = S − K), so the page shows an options-implied settlement estimate — updated every few seconds — before the print appears.
- The phase strip — the afternoon's steps — regular trading, the 15:00–15:15 reference-VWAP window that anchors the auction's price band, order entry with the index frozen, the print and the F&O tail to 15:40, then closed — with the current one lit and a countdown to the next step during the session.
- Auction impact, basis and tail flow — the cards under the strip: how far the print landed from the freeze level; the gap between the print and futures-implied cash; the futures basis before the freeze and after the print; and the call, put and futures open interest added or shed between the print and 15:40. Qty or Lots at the top switches the open interest units.
- Reversion history — for each session, the freeze, the print, the impact, futures-implied cash, the next day's open and the verdict — whether that open landed nearer the auction print (print held) or nearer futures-implied cash (print faded); EXP marks an expiry day and the chip above counts how many prints faded. This is the dataset that answers whether the print is information or noise. Click any row to replay that session.
Frequently asked questions
A call auction that sets the official closing price on NSE and BSE, live since 3 August 2026. Continuous trading in the underlying stocks ends at 15:15, orders are collected during a freeze window, and the auction's equilibrium price becomes the official close around 15:28–15:30. Equity derivatives trade until 15:40.
During auction order collection no indicative index value reaches the data feeds on either exchange, so they hold the last continuous value. The index then jumps straight to the auction-derived level in one step — the reprint you see near 15:28–15:30 is the auction result, not a trade.
Yes. The auction matches closing order imbalances, so the print can land far from the frozen tape — the first CAS session closed +200.95 points above the pre-freeze level, higher than the day's entire traded range, while futures traded roughly 180 points below the print. This page measures that divergence every session.
Yes — BSE launched CAS the same day as NSE, 3 August 2026. SENSEX's first auction prints: −38.10 on day one, then +104.39 on 4 August, landing 115.7 points above where SENSEX futures said cash should be — the same divergence pattern as NIFTY (BANKEX printed +150.88 the same day). Switch the index selector on this page to SENSEX or BANKEX to track the BSE sessions.
Final settlement of expiring index options equals the underlying's official close — the auction print. On the 4 August 2026 expiry the print landed 151 points above the frozen tape: puts that looked in-the-money on frozen screens settled worthless, and calls up to three strikes above the tape settled in-the-money. SENSEX weekly options settle the same way against BSE's auction print on Thursday expiries. On expiry afternoons this page shows a live options-implied settlement estimate while the tape is frozen.
Overnight gap, pivot and percentage-change formulas anchor to the official close. When the auction prints away from where the market actually traded, those numbers inherit the distortion — a session can open 'gap down' against the print while being flat against the continuous market. The reversion table here quantifies it per session.
The closing auction mechanism is unchanged since launch. The same January 2026 circular restructured the morning pre-open into an Open Auction Session from 7 September 2026, on both NSE and BSE, so it works like CAS: 9:00–9:05 takes market and limit orders, 9:05–9:10 is limit-only with a random close between 9:08 and 9:10, matching runs 9:10–9:12, then a buffer into the 9:15 open. OIData tracks it on the Opening Auction page, which also records whether each closing print faded at the next open. SEBI has left the door open to extending CAS beyond F&O stocks in a later phase; no date is announced.