The closing price is now struck in an auction: what changed on 3 August 2026

What actually changed

The SEBI circular opens by describing the method it is replacing, in the present tense: the closing price of stocks in the equity cash segment is determined on the basis of the volume weighted average price of trades executed during the last thirty minutes of the continuous trading session. That sentence was accurate on the day it was written and is no longer accurate for a large set of stocks.

Two documents fix the date it stopped being accurate. The SEBI circular states that the framework shall be implemented in the cash segment from 3 August 2026. NSE's notice to members says the matching changes in the equity derivatives segment shall be effective in live from the same date, after a mock trading session on the Saturday before.

The closing price did not move by a small amount. It changed category — from a summary of trades already done to a price discovered in an auction.

An auction price is not an average

A volume-weighted average price describes trades that have already happened. Every trade in the window goes into it, each at whatever price it was done at, weighted by its size. Nobody necessarily traded at the average at all — it is one figure standing in for many different prices.

An equilibrium price is the other kind of number. Orders are collected first and nothing executes while they are being collected. Then the system looks for the one price at which the largest quantity can be matched. That price becomes the closing price, and every trade in the auction is executed at it: one price, not many.

Which price that is, is not left to judgement. The circular sets out the ladder in order:

1. The price at which the maximum volume is executable.
2. If more than one price ties on volume, the price leaving the smallest unmatched quantity in absolute terms.
3. If prices still tie, the one closest to the reference price.
4. If the reference price sits exactly midway between the tied pair, the reference price itself becomes the closing price.
5. If no equilibrium price is discovered at all, the reference price becomes the closing price.

The reference price is not a guess either. It is the volume-weighted average of the trades done in the stock between 3:00 pm and 3:15 pm IST. So an average of past trades still exists inside the mechanism — but as the anchor the auction is measured against and the fallback when the auction yields nothing, rather than as the answer.

An average answers "what did the last stretch of trading work out to". An equilibrium price answers "at what single price can the most shares change hands right now". Those are different questions, and they have different answers.

The four stages, and the rules inside them

The auction is a session in its own right, not a tail on the end of continuous trading. It has four stages, and the ones a participant can act in are shorter than the session as a whole.

The third stage does not end on the clock. It shuts at an instant the system picks at random between 3:28 pm and 3:30 pm IST, so the exact moment order entry closes is not knowable in advance.

• Only limit orders and market orders are accepted, and both count towards the equilibrium price.
• Quantity cannot be hidden. An order must be disclosed in full, so iceberg orders are not accepted.
• Orders that rest until a trigger price is reached are not accepted in the auction, and are not carried into it from continuous trading either.
• Unexecuted limit orders from continuous trading are carried into the auction, unless their price falls outside the band applying inside it. They hold higher time priority than orders placed during the auction — and modifying one gives that priority up.
• Market orders are matched first: against each other in time order at the equilibrium price, then against limit orders in price-time order, with the remaining limit orders matched among themselves.
• The price band inside the auction is plus or minus 3% of the reference price.

While the auction runs, the exchange publishes the indicative equilibrium price, the cumulative buy and sell quantity, the imbalance at the equilibrium price, the imbalance counting only market orders, and an indicative index. That is a deliberately different information set from continuous trading, because there is no last traded price to publish while nothing is executing.

The clock at the end of the day

Every boundary below is set by a numbered paragraph of one of the two circulars, and the fourth column says which. A timetable written before August 2026 gets these boundaries wrong, because it has only one closing time to show.

The first row is the one that surprises people who read only the timings. The exchange did not just add a session; it restated which half hour counts as the last half hour of continuous trading for the price-band framework, moving that definition earlier to sit before the auction begins.

There is no longer a single time at which "the market closes". There are several, and which one applies depends on the segment — and inside the cash segment, on the individual stock.

Only some stocks, which is why the index carries two values

The rollout is phased, and both circulars say so in the same words: initially, the closing price of stocks in the cash segment on which derivative contracts are available shall be determined based on the auction. Every other security keeps the old method — the volume-weighted average of the last thirty minutes of continuous trading.

That has a consequence the exchange spells out. An index can hold constituents on both sides of the phase line, so while the auction is running some of its constituents are in the auction and the rest are still trading continuously. The exchange therefore disseminates two numbers: the actual index value, computed from last traded prices, and an indicative index close, computed from the indicative equilibrium price for stocks in the auction and from a volume-weighted average from 3:00 pm onwards for the stocks that are not.

The number that settles an expiring contract

This is why the change reaches people who never place an order in the cash segment. The same SEBI circular modifies the master-circular paragraph that defines a settlement price: the settlement price shall be the closing price of the underlying index on the day of expiry, and the closing price of the underlying index shall be based on the closing price of the constituents of the underlying index.

The parallel paragraph for stock derivatives is modified the same way: those contracts settle at a price calculated by the clearing corporations based on the volume-weighted average of the closing prices of the stock in the cash segment across all stock exchanges.

So the chain runs in one direction. The auction sets a constituent's closing price. The constituents' closing prices set the index's closing price. The index's closing price on expiry day is what an expiring contract settles at. The mechanism at the head of that chain did not exist in the cash segment's close before this year.

Expiry-day settlement did not change its definition. What changed is where the closing price that definition points at comes from.

What did not change, and one date that has not arrived

• The closing price in the futures and options segment itself. The exchange's guidelines record that it continues to be determined by the existing mechanism.
• The closing price of securities outside the first phase, which is still the volume-weighted average of the last thirty minutes of continuous trading.
• Option price bands, which the exchange states are unchanged across the whole trading day, 9:00 am to 3:40 pm, the auction included.

The same SEBI circular also rewrites the pre-open session, and gives that half of itself a different implementation date: 7 September 2026. From that date the pre-open runs as four stages inside 9:00 am to 9:15 am — order entry for limit and market orders from 9:00 am, limit orders only from 9:05 am with a random close in the last two minutes, matching from 9:10 am for two minutes, and the transition of orders into continuous trading from 9:12 am for three minutes.

Limits, honestly stated

• This post describes what the circulars say. It does not describe how any particular broker exposes the auction in an order window, which varies.
• The first phase is defined by a property — a stock having derivative contracts available on it — not by a fixed list published here. That property changes as contracts are introduced and withdrawn.
• Operating detail sits in standard operating procedures the exchanges and clearing corporations were directed to write, and later circulars can amend any of this. Each source below carries the date it was last checked.
• This is a description of market structure. It is not advice, and nothing here says what anyone should do about it.