Closing auction session (CAS): why candles go silent at 3:15 pm, and what the tape still shows
Since Monday 3 August 2026, the closing price of every stock that has futures and options on NSE and BSE is set by a closing auction session (CAS). Continuous trading in those stocks now ends at 3:15 pm. The candles on your chart go quiet, but the order book does not, and the official close often lands somewhere the last candle never traded.
Where the rule comes from
SEBI introduced the closing auction by circular on 16 January 2026. NSE set out the price-band rules in circular 38/2026 (18 March 2026) and BSE published the detailed operating guidelines on 10 June 2026, with trading from 3 August 2026. It is being phased in, starting with F&O stocks; every other stock still trades continuously until 3:30 pm.
The timetable, minute by minute
| Time (IST) | What happens |
|---|---|
| 9:15 – 3:15 | Continuous trading, as before. |
| 3:15 – 3:20 | Transition. The reference price is set (the VWAP of trades from 3:00 to 3:15), with a ±3 % price band around it. Pending stop-loss and iceberg orders are cancelled. |
| 3:20 – 3:25 | Limit and market orders can be added, changed or cancelled. No trades. |
| 3:25 – 3:30 | Limit orders only. Order entry stops at a random moment in the last two minutes. No trades. |
| 3:30 – 3:35 | Matching. Every executable order trades at one price, the equilibrium price, which becomes the official close. |
| Until 3:40 | Futures and options keep trading. Stock futures carry a ±3 % band aligned with the auction from 3:15. |
Timetable from BSE's operating guidelines; NSE runs the same SEBI framework, and our NSE tape below matches it.
What the tape shows: the candles stop, the book keeps moving
We record every trade and every change in the top five levels of the order book for about 210 NSE F&O stocks. Here is what that record shows, minute by minute, across all of them for the five sessions from 7 to 11 September 2026:
| Minute | Trades | Order-book updates |
|---|---|---|
| 3:13 – 3:14 | Every stock, as normal | Every stock |
| 3:15 | The last continuous trades | Every stock |
| 3:16 – 3:19 | None | None at all: the feed goes completely quiet |
| 3:20 – 3:27 | None | Every stock, every minute, about 9 updates a minute on a large stock |
| 3:28 – 3:30 | One auction trade per stock arrives | Every stock |
That is why a one-minute chart looks dead after 3:15: a candle needs trades, and there are none. Underneath, orders are arriving, being changed and being pulled for ten minutes. The auction trade then reaches our feed between 3:28 and 3:30, because order entry stops at a random moment in its last two minutes and matching starts immediately after.
One stock, one day. On Friday 11 September 2026 RELIANCE traded normally until 3:14, printed once at ₹1,263.00 at 3:15, went silent from 3:16 to 3:19, showed order-book updates with no trades from 3:20 to 3:28, and then printed the auction at ₹1,257.50, 0.44 % below its last continuous trade.
Why NIFTY and SENSEX freeze after 3:15
Every NIFTY 50 and SENSEX stock has futures and options, so every constituent goes into the auction at 3:15. During the auction the exchange calculates the live index from each stock's last continuous-session price, so the index stops moving. It also publishes a separate indicative closing value. When the auction matches, the official close arrives in one step.
Across 29 sessions from 3 August to 11 September 2026 (index-rebalance day 31 August left out), NIFTY's official close landed an average 47 points away from the index at 3:14, at least 50 points away on 9 of them, above it on 20 and below it on 9. The first day of the auction was the largest: +199.95 points (24,574.35 to 24,774.30) on 3 August. On BSE the same freeze shows on SENSEX; on 13 August its one-minute index sat flat from 3:15 and then jumped 218 points (77,861.48 to 78,079.96) with the auction print.
| Session | NIFTY at 3:14 | Official close | Change | Change % |
|---|---|---|---|---|
| 1 September 2026 | 23,984.55 | 24,055.80 | ▲ 71.25 pts | ▲ 0.30 % |
| 2 September 2026 | 23,887.25 | 23,914.45 | ▲ 27.20 pts | ▲ 0.11 % |
| 3 September 2026 | 23,910.85 | 23,873.45 | ▼ 37.40 pts | ▼ 0.16 % |
| 4 September 2026 | 23,933.00 | 23,897.70 | ▼ 35.30 pts | ▼ 0.15 % |
| 7 September 2026 | 23,761.10 | 23,779.15 | ▲ 18.05 pts | ▲ 0.08 % |
| 8 September 2026 | 23,648.40 | 23,635.10 | ▼ 13.30 pts | ▼ 0.06 % |
| 9 September 2026 | 23,465.00 | 23,431.50 | ▼ 33.50 pts | ▼ 0.14 % |
| 10 September 2026 | 23,392.35 | 23,477.80 | ▲ 85.45 pts | ▲ 0.37 % |
| 11 September 2026 | 23,433.70 | 23,398.10 | ▼ 35.60 pts | ▼ 0.15 % |
How far the official close lands from the last trade
For each F&O stock we compared the official closing price with its last continuous trade at or before 3:15 pm. Over 21 sessions from 13 August to 11 September 2026 (4,392 stock-days, index-rebalance day 31 August left out):
- The median gap was 0.22 %; the average 0.27 %.
- 44 % of closes landed at least 0.25 % away, 15 % at least 0.5 % away and 1 % at least 1 % away.
- The close was above the last trade 55 % of the time and below it 45 %.
- The largest gaps: CONCOR −3.13 % (₹509.00 to ₹493.05, 27 August), BAJAJHLDNG +2.12 % (26 August), ALKEM +1.97 % (7 September).
- On the index-rebalance day, 31 August, the average gap was 1.5 % and 65 % of stocks closed at least 0.5 % away: rebalancing orders go into the auction.
What this changes for an intraday trader
- Your chart's last candle is not the close. Tomorrow's gap is measured from the official close, which can sit well away from where the 3:15 candle ended.
- Stop-loss orders do not survive 3:15. Pending stop-loss and iceberg orders are cancelled when continuous trading ends, and limit orders outside the ±3 % band are cancelled too.
- Futures are the live market from 3:15 to 3:30. Stock and index futures keep trading until 3:40 while the cash stocks are in the auction, so price discovery in those minutes happens in futures.
- The auction has a single price. Everyone who trades in it gets the same equilibrium price, and market orders are matched before limit orders.
What our data cannot tell you yet. During the auction the exchange also publishes an indicative equilibrium price and the buy-sell imbalance. We record the order-book updates in those minutes but do not yet decode those indicative fields, so we cannot say which way the auction was leaning before it matched. We will write that up once we can.
Sources
- NSE circular 38/2026, NSE/CMTR/73362 (18 March 2026): reference price, ±3 % band, order types, closing price, index dissemination during CAS.
- BSE notice 20260610-41 (10 June 2026): session timetable, equilibrium price rules, effective date Monday 3 August 2026.
- Tape figures: TBTflow's own NSE tick and order-book record (trades and five-level depth), 7 August to 11 September 2026.
Quick questions
What is the closing auction session in the stock market?
What are the CAS timings?
Why is the NIFTY chart flat after 3:15 pm?
Why is the closing price different from the last traded price?
Are stop-loss orders allowed in the closing auction session?
Does the closing auction apply to all stocks?
Closing auction session kya hai?
This page describes market structure and market activity. It is not investment advice and not a recommendation to buy or sell any security. TBTflow is not registered with SEBI.
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