3:15–3:35 pm
The closing auction session
Since 3 August 2026 the closing price of stocks with derivative contracts is set by a 20-minute auction at the end of the day — or, if the auction finds no price, by its reference price.
The schedule
Closing Auction Session (CAS) operates as a separate session of 20 minutes from 3:15 pm to 3:35 pm on all trading days, as under:
NSE’s table (times and remarks as printed).
| Session | Time | Remark |
|---|---|---|
| Reference price calculation / Transition from Continuous Trading Session (CTS) to CAS | 03:15 pm - 03:20 pm | - |
| Order Entry Period | 03:20 pm -03:25 pm | Order entry, modification and cancellation for both limit and market orders. |
| Order Entry Period | 03:25 pm -03:30 pm (*) | Order entry, order modification, order cancellation period only for limit orders. No order entry/ modification/ cancellation allowed for market orders. (*) system driven random closure in the last 2 minutes. |
| Order Matching & trade Confirmation Period | 03:30 pm -03:35 pm | (*) Order matching period will start immediately after completion of order entry period. Order matching and trade confirmation. |
| Transition period | 03:35 pm – 03:50 pm | Transition from CAS to post close session. |
| Post Close Session | 03:50 pm - 04:00 pm | Except for the session timings, no change in current modalities of the post close session mechanism. |
Phase 1: Applicable only to stocks in the cash segment on which derivative contracts are available.
Rules of the auction
Reference Price: The reference price of a stock in CAS in the cash segment is determined based on the VWAP of the trades executed in the stock during the period 3:00 p.m. to 3:15 p.m.
Price Band: Price band applicable during CAS is +/- 3% from the reference price of the stock.
Order Types: Only limit orders and market orders are allowed. Stop loss orders and iceberg orders are not allowed.
For securities on which CAS is applicable, closing price shall be determined based on the equilibrium price determination mechanism in CAS.
In case the equilibrium price is not determined, then reference price calculated as per point 2.1 & 2.2 above shall be the close price.
In plain words
The auction starts from a reference price — the volume-weighted average price of trades between 3:00 and 3:15 pm — and orders must sit within 3% of it either way. Its equilibrium price becomes the stock’s closing price for the day; if no equilibrium price is determined, the reference price is the close.
A tie decided by the reference price (invented stock)
In case there is more than one price at which the maximum volume is executable and they have same minimum order imbalance quantities, the equilibrium price shall be the price closest to the reference price.
A sample stock’s reference price is ₹250.40. The auction book (tested at the prices in the book, as above):
Buy orders
- ₹250.50: 400 shares
- ₹250.00: 300 shares
Sell orders
- ₹250.00: 400 shares
- ₹250.50: 300 shares
Both prices let 400 shares trade with the same imbalance of 300.
| Price | Buy at or above | Sell at or below | Tradable | Imbalance |
|---|---|---|---|---|
| ₹250.00 | 700 | 400 | 400 | 300 |
| ₹250.50 | 400 | 700 | 400 | 300 |
In plain words
Volume ties and imbalance ties, so the third test decides: ₹250.50 is 0.10 from the reference price and ₹250.00 is 0.40 away. The closing price is ₹250.50. (Had the reference been exactly midway, at ₹250.25, the reference price would apply under NSE’s mid-value rule.)
After the auction
Except for the session timings, no change in current modalities of the post close session mechanism.