Old Strategies Buried Alive: How the New Closing Auction Session Disrupted Dalal Street Traders
Key Takeaways
- •SEBI replaced the previous VWAP-based closing price method with a brief auction-based session at the end of each trading day to improve price discovery.
- •Traders report that established end-of-day strategies have become ineffective due to increased closing price volatility under the new system.
- •Low participation in the closing auction has amplified price swings, with even modest orders having outsized effects on closing prices.
- •The closing price serves as a critical benchmark for mutual fund NAV calculations, mark-to-market margin settlements, and derivatives settlement references across Indian markets.
- •SEBI expects the mechanism to stabilize as more participants adjust their workflows, consistent with the trajectory observed in other global markets that adopted closing auctions.
Old Strategies Buried Alive: How the New Closing Auction Session Disrupted Dalal Street Traders
The new Closing Auction Session (CAS) has rattled Dalal Street, with traders reporting that long-standing end-of-day strategies are no longer functioning as expected. The Securities and Exchange Board of India (SEBI), however, remains confident that the system will improve as participation increases.
Weak liquidity and volatile closing prices have intensified concerns, forcing traders and brokerages to rapidly adapt to the new market mechanism. The closing price is a critical benchmark across Indian markets — used for mutual fund net asset value (NAV) calculations, mark-to-market margin settlements, and derivatives settlement references — meaning that volatility in this single price point has cascading effects well beyond proprietary trading desks.
What Is CAS?
The Closing Auction Session is a market structure reform introduced by SEBI for Indian stock exchanges. Under the new framework, the closing price of securities is determined through a brief auction-based session at the end of the trading day, rather than through the previous method of calculating the Volume Weighted Average Price (VWAP) over the last 30 minutes of continuous trading. The auction-based approach is designed to improve price discovery at market close and align India's closing mechanism more closely with practices in several major global markets, including the London Stock Exchange and Hong Kong Exchanges, which have long used closing auctions to consolidate end-of-day liquidity into a single transparent price.
Initial Teething Issues or Flaws?
Since implementation, market participants have reported significant disruptions. Traders have noted that established strategies — particularly those built around the former VWAP-based closing mechanism — have become ineffective. The transition has raised questions about whether the early volatility reflects temporary teething problems or deeper structural issues with the new system.
Related coverage from Economic Times includes: Dalal Street's biggest stock reform in years endures rocky first week and Distortions are inevitable: Nithin Kamath explains why new closing auction is causing wild moves in Indian stocks.
Weak Participation Intensifies CAS Volatility
Low participation in the closing auction has amplified price swings, according to traders. With fewer orders flowing into the auction session, even relatively modest buy or sell orders have had outsized effects on closing prices, contributing to the volatility that has frustrated market participants.
SEBI has maintained that broader participation will help stabilize the mechanism over time, as more traders and institutional investors adjust their end-of-day workflows to the auction format. The regulator's expectation echoes the trajectory seen in other markets that transitioned to closing auctions, where initial thin order books gradually deepened as participants became familiar with the new mechanism. For now, however, brokerages and proprietary trading desks are being forced to overhaul their closing-session strategies on the fly.
Source: Economic Times Markets
