The "Golden Rule" for cancelling a flight ticket for a full refund is to do so within the 24-hour "cooling off" period immediately after booking, as mandated by many international regulations (including the US DOT and recent 2026 DGCA revisions in India). Beyond this window, you should cancel your ticket the moment you are certain you cannot travel, as many airlines offer more flexible eCredit options the further out you are from the departure date. If the airline itself initiates a significant schedule change (typically more than 2-3 hours) or cancels the flight, you are legally entitled to a full cash refund regardless of your original ticket type. In 2026, many travelers use "flight price trackers" to monitor their routes; if a price drops significantly on a "changeable" ticket, you can often "cancel and rebook" to save money, provided you are mindful of any potential fare differences or basic economy restrictions.