_lg.webp)
From August 3, 2026, India will calculate stock closing prices in a new way. SEBI's Closing Auction Session replaces the old 30-minute average method with a short auction. Here's a simple breakdown of what changes and when.
Every stock has a "closing price" at the end of each trading day. This one number matters more than most people realise. It decides the value of the Nifty and Sensex, the NAV of your mutual funds, the final settlement price on F&O expiry day, and even your portfolio's daily P&L.
Until now, this closing price was not simply the last traded price of the day. That's because a single small trade in the last few seconds could distort it. To avoid this, exchanges have used the Volume Weighted Average Price (VWAP) of the last 30 minutes of trading (3:00 pm to 3:30 pm):
VWAP = Total value of trades ÷ Total quantity traded
This is now changing. From August 3, 2026, SEBI is introducing the Closing Auction Session (CAS) — a new way to set closing prices, starting with stocks that have active Futures & Options (F&O) contracts.
Why Is SEBI Making This Change?
In the current system, trades happen one after another throughout the day, and the closing price is just an average of the last few. SEBI wants a system where all buyers and sellers place their orders together, at the same time, in one pool. This way, the closing price reflects what everyone in the market wants at that exact moment — not just a string of separate trades.
This also helps big investors. Right now, if a mutual fund wants to buy or sell a large number of shares, it has to split the order into smaller pieces so it doesn't move the price too much. In an auction, all orders come together at once, so a large buyer can more easily match with a large seller at a fair price. This also helps index funds and ETFs track their benchmarks more accurately.
This isn't a new idea globally — big exchanges like the NYSE and LSE already use a closing auction. SEBI's move brings India in line with these markets.
What Changes for Traders and Investors
For now, stocks are split into two groups:
- Category I — stocks with active F&O contracts on NSE and BSE. These move to the new CAS system.
- Category II — all other stocks. These continue as before, using VWAP.
For Category I stocks:
- Regular trading stops at 3:15 pm instead of 3:30 pm.
- The derivatives market stays open a bit longer, until 3:40 pm.
- Stocks not under CAS keep trading normally until 3:30 pm.
If you trade intraday using MIS orders, the auto square-off time also changes from August 3, 2026:
- Equity (not under CAS): 3:25 pm
- Equity (under CAS): 3:10 pm
- Equity and index derivatives: 3:25 pm
How the Auction Works, Step by Step
Once regular trading ends at 3:15 pm for a CAS stock, here's what happens next:
| Time | What Happens | Duration |
| 3:00 pm – 3:15 pm | Regular trading continues. The exchange also calculates the VWAP of this window, which becomes the "reference price." | 15 minutes |
| 3:15 pm – 3:20 pm | No new orders allowed. The exchange sets the reference price and a price band of ±3% around it. | 5 minutes |
| 3:20 pm – 3:25 pm | Orders open again. You can place both market and limit orders. The exchange shows live updates on likely closing price and order demand. | 5 minutes |
| 3:25 pm – 3:30 pm | Only limit orders allowed now. Market orders can't be placed or changed. This window closes at a random time between 3:28–3:30 pm, so no one can time the very last order. | ~5 minutes |
| 3:30 pm – 3:35 pm | No more orders. The exchange matches all orders at one final price. This becomes the official closing price. | 5 minutes |
A few small but useful details: if you already had an open order from before 3:15 pm, it usually carries forward into the auction. The exceptions are stop-loss orders, iceberg orders, and any order outside the ±3% price band — these get cancelled automatically.
How Does the Exchange Decide the Final Price?
This is the part that sounds technical, but the idea is simple. During the auction, the exchange looks at all buy and sell orders together and checks: at which price can the most number of shares actually be matched between buyers and sellers?
That price — the one where the maximum number of shares can trade — becomes the closing price. If two prices could work equally well, the exchange picks the one where buy and sell quantities are closest to balanced. If it's still a tie, it goes with whichever price is closest to the reference price set earlier.
Quick Answers
Does this apply to every stock? No, not yet. For now, it only applies to stocks with active F&O contracts (Category I). All other stocks keep using the old VWAP method.
What time does trading stop for CAS stocks? 3:15 pm instead of 3:30 pm. The auction then runs until the closing price is fixed, usually by 3:30–3:35 pm.
Can I place an order between 3:15 pm and 3:20 pm? No. This is a short pause where the exchange sets the reference price and price band. No orders are accepted in this window.
Why is SEBI doing this? To make the closing price more accurate and harder to manipulate, and to bring India's markets in line with how major global exchanges already work.
Key Facts at a Glance
| Detail | Information |
| Effective from | August 3, 2026 |
| Applies to (Phase I) | Stocks with active F&O contracts on NSE/BSE |
| Old method | VWAP of last 30 minutes (3:00–3:30 pm) |
| New method | Auction-based matching at one final price |
| Trading end time for CAS stocks | 3:15 pm |
| Auction window | 3:15 pm – 3:30/3:35 pm |
| Derivatives market close | 3:40 pm |
| MIS square-off (CAS stocks) | 3:10 pm |
| MIS square-off (other stocks, derivatives) | 3:25 pm |
| Price band during auction | ±3% of reference price |
Disclaimer: This article is for educational purposes only and does not constitute investment advice or a recommendation regarding any specific security. Corporate action mechanics described here are general principles; actual price adjustments, ratios, and timelines vary by company and are determined by each company's board and applicable stock exchange rules. Readers should refer to official company announcements and stock exchange notifications for the specific terms of any corporate action before making investment decisions.