You can cancel now or latest upto 5 pm on 17.5.2011 to get maximum refund.
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UNUSED TICKETS ON WHICH RESERVATION HAS BEEN MADE :
(1) Subject to the provision of these rules, if a ticket on which reservation of a seat or berth has been made, is presented for cancellation, refund of fare shall be made after deducting cancellation charge from the fare...
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as follows :
(a) If a ticket is presented for cancellation more than 24 hours before the scheduled departure of the train cancellation charge shall be deducted at the flat rate of Rs. 70/- for A.C First Class/Executive Class, Rs. 60/- for A.C. 2 Tier sleeper class/ A.C. 3 Tier sleeper class/ First class/A.C Chair Car, Rs. 40/- for Sleeper class and Rs. 20/- for Second class.
(b) If the ticket is presented for cancellation within 24 hours and up to four hours before the scheduled departure of the train, cancellation charges shall be 25% of the fare subject to the min. flat rate mentioned in clause (a).
(c) If the ticket is presented for cancellation within four hours before the scheduled departure of the train and up to :
1. Three hours, when the ticket is for a destination station up to 200 KM.,
2. Six hours, when the ticket is for a destination station of more than 200 KM but up to 500 KM., and
3. Twelve hours , when the ticket is for a destination station of more than 500 KM.,
after the actual departure of the train, cancellation charges shall be 50 % of the fare subject to the min. flat rate mentioned in clause (a).