The National Stock Exchange and Bombay Stock Exchange launched their Closing Auction Session, a 20-minute auction window designed to replace the old method of calculating end-of-day prices. The result was immediate confusion among traders and an unexpected spike in the Nifty 50 Index as participants scrambled to understand the new price discovery mechanics. What actually changedFor years, India’s exchanges calculated official closing prices using a volume-weighted average price (VWAP) method across a 30-minute window. Why the confusion matters beyond equitiesMutual fund NAVs are calculated using closing prices. The VWAP method had a known vulnerability.