Guide · Market structure · Updated 2026-09-23

The official close is not the last trade, and since 3 August 2026 it is set two different ways

Any explanation of the Indian closing price written before August 2026 says it is the average price of the last half hour. Since 3 August 2026 that is true only of stocks without derivatives. For the 207 stocks that carried stock futures on every session since, a group that includes all fifty constituents of the broad benchmark index, the close has been an auction price for 36 sessions, and the change reaches past the stock itself: into the index, into how derivatives settle, into the price a fund values its holdings at that evening.

Every measured figure below was computed from the exchanges' own daily files rather than quoted, and the closing note sets out the method so the work can be redone. The worked auction is illustrative and is labelled as such.

The last trade was never the close, and now there are two closes

Until 31 July 2026 every stock in the cash market closed on one rule, which the exchange's consolidated circular NSE/CMTR/73927 of 28 April 2026 states in section 3.4: the value weighted average price of the last half hour of trading; the day's last traded price if nothing traded in that half hour; the latest available close if nothing traded all day, aligned to the stock's tick. An average over thirty minutes is deliberately hard to push. A stray print at 3:29:59 pm moves it only in proportion to its share of the half hour's volume, which is why the rule has long been described as a defence against a single order setting the close.

SEBI's circular of 16 January 2026, SEBI/HO/47/11/11(3)2025-MRD-POD2/I/2765/2026, replaced that rule in phases with a closing auction, citing practice in major markets and the weight the close carries in derivatives settlement, index computation and fund valuation. The first phase covers stocks on which derivative contracts are available on any exchange (NSE/CMTR/74466 of 29 May 2026) and went live on 3 August 2026 (NSE/CMTR/75479 of 30 July 2026). Every other stock still closes on the half hour average, so a screen showing two stocks at 3:30 pm is now showing two different kinds of number.

The two mechanisms answer different questions. The average says what a stock traded at, on balance, in its last half hour: a summary of trades that already happened. The auction says at what single price the largest number of shares can change hands among everyone who wants to trade at the close, and that price does not exist until the auction runs. Its value depends on who turned up, which is both its purpose and its risk.

Inside the twenty minutes: a transition, two entry windows, a random close, one price

For stocks with derivatives, continuous trading stops at 3:15 pm. The next five minutes are a transition in which the exchange computes each stock's reference price, the volume weighted average of its trades from 3:00 to 3:15 pm, sets a band of 3 per cent either side of it, and moves eligible orders across. Unexecuted limit orders inside the new band carry into the auction with their original time stamp and rank ahead of limit orders entered during it. Stop loss orders, iceberg orders and anything priced outside the band are cancelled, and any order sent during the transition is rejected.

Entry opens at 3:20. From 3:25 only limit orders are accepted and market orders already in the book are locked, and entry shuts at a moment the system picks at random between 3:28 and 3:30 pm, so nobody can time a decisive order to a known last second. Matching follows at a single equilibrium price, every unexecuted order is then cancelled, and the post close session from 3:50 to 4:00 pm trades only at the close already set.

Three details in the exchange's documents change what an order means here. Only limit and market orders are allowed; stop loss, immediate or cancel and disclosed quantity orders are not. Market price protection, the exchange's usual guard on market orders, does not apply during the auction (NSE/CMTR/74466, section K), so a market order is bounded only by the 3 per cent band. And execution does not follow price and time: market orders are matched against each other first, then against limit orders, and only then are limit orders matched with each other in price and time order, a demotion of queue priority worked through in the guide to queue position.

While the auction runs the exchange publishes the indicative equilibrium price, the quantity tradable at it, the cumulative buy and sell quantities, the imbalance at the indicative price with its side, and an indicative index built from the constituents' indicative prices (NSE/CMTR/73362, section 6). Equity derivatives keep trading throughout, now to 3:40 pm, with stock futures held to a band aligned with the auction's from 3:15. The same equilibrium rule sets the opening price, and the pre-open call auction guide takes it through a worked book tie-break by tie-break; the session map places both auctions in the whole trading day.

Why the close outranks every other print of the day

Of the thousands of prices a liquid stock prints in a session, one is carried forward into other people's arithmetic. SEBI's circular names the reasons in its second paragraph: the close is the reference for derivatives settlement, index computation and mutual fund net asset values, and an auction lets passive funds transact at the close and so reduce tracking error. The table traces each consumer to the rule that sends the close there.

Two rows need care. A stock derivative does not settle at one exchange's close. The clearing corporations' joint standard operating procedure, circulated as NCL/CMPT/73370 on 19 March 2026, computes a settlement price for each stock and uses it on expiry day: where auctions discovered a price on more than one exchange, the volume weighted average of those prices by the quantity each auction traded; where no auction found a price anywhere, the simple average of the reference prices. That is one step removed from the close a chart shows, and the gap is measured below. And futures are marked to market daily on their own closing price, the average of 3:10 to 3:40 pm, so the cash auction reaches futures and options through expiry rather than through every day's margin. The guide to pin risk shows what a settlement price nobody can trade at does to a position near a strike.

A single clearing price is set by the marginal order, not by the crowd

The difference between an average and an auction is clearest when one participant must trade a large quantity at the close, which is what an index fund does when its benchmark rebalances. Under the average, a trade pulls the close by its share of the window's volume times its distance from the rest of the window. Put one print of 25,000 shares at 1,005 into an illustrative half hour that traded 300,000 shares at an average of 1,000, and the close moves to 1,000.38. Under the auction the same order acts differently in kind. A market order sits on the demand side at every price, so it lifts the whole demand curve, and the price rises until enough sellers are reached.

Read the table from the top. The original book clears at the reference price, 1,000, matching 14,000 shares. Add a market buy of 25,000 shares and the indicative price moves to 1,005, +0.5 per cent, and every share that trades in the auction, including those of buyers who had bid 1,000, trades at 1,005. The imbalance at the indicative price is now 2,000 sell: at 1,005 slightly more shares are offered than bid, because the price has climbed to where sellers are. The pressure shows in the market order imbalance, 25,000 shares to buy, one of the figures SEBI's circular lists for dissemination during the auction (paragraph 4.12.4). That publication is deliberate, and the third row shows why: sellers who see it and offer 15,000 shares between 1,002 and 1,004 pull the price back to 1,003, and the buyer is filled in full at a better price than without them. The auction turns the arrival of a large order into an invitation for the other side to meet it.

The last row is the failure mode. A market buy of 60,000 shares exceeds all 41,000 shares offered inside the band. The price rises to the highest offer in the book, 1,025, not to the band edge, because the rule stops at the price that clears the most shares with the least left over and nearest the reference. 22,000 shares of the order go unfilled and are cancelled when the auction ends. The band guarantees the close cannot run beyond 3 per cent. It does not guarantee a large order is filled, and a market order in the auction can be neither withdrawn after 3:25 nor protected by a price limit.

Measured: the last trade and the close, before and after 3 August

The exchange's daily security file carries both the last traded price and the close for every stock in every session, so the change can be measured. Files for 1,164 sessions from 3 January 2022 to 22 September 2026 were read. The stocks with derivatives are the 207 that carried stock futures on every one of the 36 auction sessions, taken from the exchange's daily derivatives files; the comparison group is every equity series stock that carried none at any session from June to September 2026, 2,569 of which traded in the auction period.

Before the change the last trade and the close were rarely the same number: on 2.9 per cent of stock sessions for the stocks with derivatives, with a median gap of 0.13 per cent and one session in ten beyond 0.42 per cent. From 3 August the two agree on every one of the 7,452 stock sessions, and on all 7,526 when each session is checked against that day's own derivatives list instead of a fixed panel. The relationship did not weaken. It became an identity, because the auction's trades are the last trades of the day and all of them print at the closing price. For stocks still on the average nothing moved: a median gap of 0.25 per cent before and 0.24 after. The small rise in their exact matches, 7.0 to 8.1 per cent, comes from thinly traded sessions, where a stock that did not trade after 3:00 pm closes on its last trade by rule.

Two consequences follow. For the stocks with derivatives the last traded price column stopped being an independent observation on 3 August, silently, under an unchanged header. The file can no longer show how far the auction moved the price from the last continuous trade at 3:15, and none of the daily capital market reports the larger exchange lists carries that number or the reference price. For every other stock the gap remains, and it is a question of how much the stock trades.

The median gap falls from 0.38 per cent in stocks that traded between 0.1 and 1 crore to 0.16 per cent in those that traded 100 crore or more, and its size relative to the day's range roughly halves. The thinnest row breaks the pattern for a mechanical reason: a stock that trades a handful of times a day often has no trade after 3:00 pm, so its close is its last trade by definition, 17 per cent of the time. When it does trade in the window, an average of a few scattered prints can sit far from the last one.

The close can now be the day's extreme, and the next morning takes some of it back

An average of half an hour of trades equals the day's high only if every trade in the window printed at the high, which in a liquid stock does not happen. A single clearing price has no such restriction. In the six months before the change the close of the 207 stocks with derivatives was never the day's high or low, in 25,235 stock sessions. Since 3 August it has been the day's high in 8.3 per cent of stock sessions and the day's low in 7.4 per cent, about one close in six.

The index inherits it. The broad benchmark index is computed from the closing prices of its fifty constituents, and every one of them now closes through the auction. In 3,351 sessions from 1 January 2013 to 31 July 2026 it never closed at its day's high or low. In the 36 auction sessions it has done so 9 times, and the banking index 7 times. On a chart of either index a daily candle now ends at the tip of its range about one session in four, which is a statement about the auction more than about how the afternoon traded.

The next morning measures how much of an auction close was pressure. Take the close's distance from the day's average price, which holds both the afternoon's genuine move and anything the auction added, and ask how much of it the next open carries on or takes back. On the average close the open carried about a fifth further in the same direction, +0.21, because an average of 3:00 to 3:30 lags a price that is still moving. On the auction close the open takes about a fifth back, -0.22. Stocks without derivatives, still on the average, barely changed.

The intervals come from resampling whole sessions, because stocks move together overnight and a count of stock sessions overstates the evidence; even so, the difference between the two groups' changes, -0.42, excludes zero on 35 auction sessions. The sign is the finding. Part of what an auction close adds to the day is temporary, and the next pre-open auction removes it. That does not make the auction a worse price, only a different one: current to the minute rather than smoothed over thirty, and carrying whatever imbalance cleared at 3:30.

Two exchanges, two auctions, one settlement price

Each exchange runs its own closing auction on its own order book, with its own reference price and band (questions 11 and 55 of the exchange's frequently asked questions). Before August both closes were half hour averages of the same stock trading at the same time in two linked markets, and they agreed within a few basis points. They no longer have to.

For stocks with derivatives the median gap between the two exchanges' official closes rose from 2.9 basis points to 17.1, and the share of stock sessions more than half a per cent apart from 0.08 per cent to 16.1 per cent. It was widest in the first days, a median of 33 basis points across the first five auction sessions, and has run near 13 over the last fifteen, still several times its old level. Liquidity changes the size of the gap only at the margin. Split the stocks into thirds by turnover, and the median gap after 3 August was 18.4 basis points for the least traded third, below about 132 crore a day, and 15.3 for the most traded, above about 248 crore, against 3.5 and 2.4 before; the close landed on the day's high or low in 14.5 and 16.9 per cent of their sessions. The jump is the mechanism, two independent auctions, not thin trading. For liquid stocks still closing on the average on both exchanges nothing changed: 5.1 basis points before, 5.0 after.

The settlement price blends the two auctions by quantity, and because the larger exchange's auction usually carries most of it, the blend usually sits close to that exchange's close. Usually is the operative word. The share of stock sessions on which the two were equal fell from 87.3 to 38.4 per cent. At the June and July expiries 189 of 211 and 185 of 210 expiring stock futures settled at exactly the larger exchange's close. At the August expiry, the first under the auction, 74 of 208 did, 43 settled more than a basis point away and the largest gap was 25 basis points. Anyone checking an expiring position against one exchange's close was checking it against a number the contract does not settle on.

The tail is where the arithmetic bites. On 27 August 2026 the second exchange's auction closed 8 stocks between 1.9 and 3.3 per cent below the larger exchange's close for the same stocks, and because that auction carried real quantity, their settlement prices moved 1.1 to 1.8 per cent away from the price on the larger exchange's screen, in every case to below the lowest price the larger exchange printed all day. All 8 are constituents of the banking sector indices. On no other auction session did any of the 207 stocks' settlement price sit more than 1 per cent from that close. The files show what happened, not why. They do show that a price discovered in a thinner book, bounded only by its own 3 per cent band, can pull a settlement price to a level the larger market never traded at.

When the auction finds no price

The failure rule is written into the circular. If no equilibrium price is discovered, the reference price, the average of 3:00 to 3:15 pm, becomes the close; if the stock did not trade in that window, the day's last trade; if it did not trade at all, the previous close (SEBI circular, paragraphs 4.3 and 4.6.6; NSE/CMTR/73362, section 5.1.1). For settlement the clearing corporations then take the simple average of the exchanges' reference prices. Two wider exits apply: no auction is held on a day the market closes early on an index circuit breaker, when every stock closes on the old average or its last trade, and none for a stock on the ex-date of a scheme of arrangement whose price was not set in the special pre-open session (NSE/CMTR/74466, sections A and C).

The exchange does not announce individual failures; its frequently asked questions say the case is covered by the rule and will not be disclosed separately (question 12). The daily file leaves a trace anyway. A failed auction has no trades, so the last trade would be a continuous trade from before 3:15 pm and would almost never equal the reference price to the paisa. In 7,526 eligible stock sessions the last trade and the close matched every time, so the file shows no sign of a failed auction among these stocks in 36 sessions. It also shows eligibility moving with the derivatives list: the 3 stocks whose contracts began on 26 August 2026 closed by auction from their first session with derivatives, and the one whose contracts lapsed after the August expiry kept an auction close for 2 more sessions before reverting to the half hour average.

What changes for an order placed near the close

For stocks with derivatives the continuous market now ends at 3:15 pm, and the price on the screen at 3:14 is not a price anyone can deal at in the close, which can land anywhere within 3 per cent of the 3:00 to 3:15 average. There is no market on close or limit on close order type (question 20). The nearest thing is a market order entered between 3:20 and 3:25, which is then locked, unprotected by a price limit, and filled at whatever price clears, or only in part if the band binds. A limit order entered in the auction can be revised until the random close, with the published imbalance showing which side is short. For every other stock the same order at 3:25 pm still meets a continuous market. How to read the imbalance and take part in the auction deliberately is a subject of its own.

The rules are still moving

SEBI's consultation paper of 12 September 2026 reviews the auction after its first month. It reports that derivatives activity stayed concentrated near the close: on expiry days, premium traded in expiring benchmark index options on the larger exchange averaged ₹189.82 crore a minute between 3:20 and 3:30 pm, against ₹126.31 crore a minute between 3:00 and 3:30 pm before the auction. It sets out seven proposals: settle expiring derivatives either on a blend of the last 30 minutes of continuous trading and the auction, weighted by traded value, or on the continuous half hour alone for at least a year; stop publishing the indicative index during the auction; run the auction after 3:30 pm, or keep it after 3:15 pm, with the transition cut to about a minute and derivatives trading for five minutes after the auction rather than ten; forbid cancelling auction orders priced more than 1 per cent from the reference price; and carry the unexecuted part of iceberg orders into the auction in full. Comments are invited until 3 October 2026. Any description of the close, this one included, should be read with its date.

What the close is for

The official close is a constructed number, and since August it is constructed two ways under one column name. For a backtest, a close to close return that straddles 3 August 2026 compares an average with an auction, a seam that the guide to the bhavcopy's fields and the guide to cleaning outliers treat from the data side. For a chart, a daily candle whose close sits at its extreme is often a fact about ten minutes of auction, not about the afternoon. For a derivatives position, the settlement price is a blend of two auctions that neither exchange's screen displays. Knowing which close a number is before reading what it says is the kind of judgement about market structure the curriculum is built to teach.