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Closing AuctionSession

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.

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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 — for NIFTY, SENSEX, BANKNIFTY, BANKEX and the other tracked indices via the index switcher.

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 before the print appears.
  • Reversion history — for each session, whether the next day's open landed nearer the auction print or nearer futures-implied cash. This is the dataset that answers whether the print is information or noise.

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 at around 15:28. Equity derivatives trade until 15:40.

During auction order collection no indicative index value is disseminated on either exchange, so data feeds 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 an 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.

Learn how to read it

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