Closing Auction Session (CAS) – A Step by Step Guide
Starting August 03, 2026, SEBI is introducing a Closing Auction Session (CAS) for
equity shares on which Futures & Options (F&O) contracts are available.
This changes how the closing price is determined and how trading works after 3:15
PM for these eligible shares.
Whether you are a delivery investor, intraday trader or F&O trader, this guide
explains what changes, how the new process works, and what it means for your trades.
What is the Closing Auction Session?
Every trading day, a stock has a closing price. This price is important because
it is used for activities such as derivatives settlement, index calculation, ETF
rebalancing etc.
Until now, the closing price of eligible shares has been calculated using the
Volume Weighted Average Price (VWAP) of trades executed during the last 30 minutes
of regular trading.
Starting August 03, 2026, this will change for equity shares on which Futures &
Options (F&O) contracts are available.
Instead of calculating the closing price from trades executed during the last 30
minutes, the exchange will conduct a Closing Auction Session (CAS) after regular
trading ends. During this auction, eligible buy and sell orders are collected and
matched to determine a single closing price.
Does This Apply to All Stocks?
Not in Phase 1. To ensure a smooth structural transition, the implementation is
divided by asset categorization:
- F&O Securities: CAS applies exclusively to equity cash segment shares that
have active derivative contracts available (e.g., Nifty 50 or highly liquid
large-cap counters). Continuous trading for these stocks stops early at 3:15
PM.
- Non-F&O Securities: All other cash segment stocks will face no immediate
modifications. You can continue trading them via continuous matching all the
way until 3:30 PM as you do today.
How does Trading Day change?
For CAS-eligible shares, the last part of the trading day will now follow a
different schedule.
CAS trading day schedule
| Time |
What Happens? |
| 9:15 AM to 3:15 PM |
Regular trading (Only CAS Eligible stocks) |
| 3:15 PM to 3:20 PM |
- > This is the transition period. The exchange calculates the Reference Price.
- > Exchange will not accept any order during this session
|
| 3:20 PM to 3:25 PM |
- > Market and Limit Orders can be placed, modified or cancelled.
- > Orders will be allowed in only Delivery and MTF product.
- > SL, IOC and Diclose Qty orders won't be allowed
|
| 3:25 PM to Random Close (between 3:28 PM and 3:30 PM) |
- > Only Limit Orders can be placed, modified or cancelled.
- > No new order placement, modification or cancellation is allowed for Market Orders.
- > Orders will be allowed in only Delivery and MTF product.
- > SL, IOC and Diclose Qty orders won't be allowed
|
| 3:30 PM to 3:35 PM |
Orders are matched, and the official closing price is determined.
No new orders can be placed during this time. |
| 3:40 PM |
Derivatives Trading Session closes. |
| 3.50 PM to 4.00 PM |
Post close session for Equity segment |
Intraday Square-off Timing from 3 August 2026
Intraday square-off timing from 3 August 2026
| Time |
Applicable To |
Remarks |
| 2:45 PM |
All Equity & F&O Intraday |
From 2.45 PM all fresh intraday orders and position conversions will be blocked |
| 3:00 PM |
Equity Intraday & Equity Cover for CAS Scrips |
3.00 PM will be revised Auto Square off time (Moved up from 3:15 PM). |
| 3:15 PM |
A. F&O Intraday & F&O Cover (All Scrips)
B. Equity Intraday & Equity Cover for Non-CAS Scrips
|
Auto square off will be at 3.15 PM (Unchanged) |