You can cancel now also or file TDR after charting,but remember to get full refund the request should be made online before departure of the train.
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Go thru the New Rules:
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Non-commencement or...
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missing of journey due to late running of trains:
• No cancellation charge or clerkage shall be levied and full fare shall be refunded to all passengers holding reserved, RAC and waitlisted tickets, if the journey is not undertaken due to late running of the train by more than three hours of the scheduled departure of the train from the station commencing the journey subject to condition that the ticket is surrendered upto the actual departure of the train instead of existing 3/6/12 hours for distance 200 kms/200-500 kms/500 Kms and above after the actual departure of the train
• in case of e-tickets, the TDR is filed o¬nline before the actual departure of the train for availing full refund.
• In case the ticket is cancelled or surrendered or if the request for refund of fare is filed online after the actual departure of the train, no refund of fare shall be admissible.