When is seat availability updated?

Seat availability is updated in real time on the IRCTC system as soon as any transaction happens. The moment a passenger books, cancels, or modifies a ticket, the system recalculates and displays the new availability. Charts for a train are prepared approximately four hours before departure, after which no further online bookings are accepted and the seat count becomes final. For Tatkaala bookings, availability updates exactly one day before the journey date when the Tatkaala quota opens. During high-demand periods the system refreshes every few seconds, so you may see the count change even while comparing trains.