The cancellation window that most people miss by hours
Indian Railways grades refunds by how far in advance you cancel. Cancel a confirmed AC-class ticket more than 48 hours before departure and the deduction is a flat clerkage charge, ₹240 for AC classes, ₹60 for sleeper. Wait until the 12-to-48-hour window and the deduction jumps to 25 percent of the base fare. Inside 12 hours but before chart preparation, it rises to 50 percent. After chart preparation, an online cancellation gives you nothing at all for a confirmed ticket. The window that catches most people is the 12-hour mark, which often falls in the middle of the night before a morning train. Set an alarm. The difference between cancelling at 11:58 PM and 12:01 AM on a Rajdhani ticket can be several hundred rupees.
What actually happens to a waitlisted ticket if you do nothing
A waitlisted ticket booked through IRCTC that does not confirm before chart preparation is automatically cancelled by the system, and the refund, minus a small clerkage charge, is credited back to the source account within a few working days. No action is required from you. Where passengers lose money is on counter-bought waitlisted tickets: those are not auto-cancelled. You must physically surrender the ticket at the station before departure to claim the refund. Pocketing a counter waitlisted ticket and boarding a different train means you lose the full fare. The rule is asymmetric, and most passengers do not know it is asymmetric.
The TDR and when filing one actually works
A Ticket Deposit Receipt is the mechanism for claiming a refund when you could not cancel before the train left, because the train was late, because you were ill, or because a confirmed ticket went uncharted due to a system error. The TDR must be filed within 72 hours of the scheduled departure on IRCTC. Filing it does not guarantee a refund; it opens a claim that the Zonal Railway examines. Refunds on TDRs for train-delay reasons are generally processed, but TDRs filed because a passenger simply missed the train are routinely rejected. The rule that most people discover too late: a TDR cannot be filed at all for tickets where the passenger was marked as having travelled. If a TC has marked your PNR as travelled, correctly or not, the TDR window closes.
Partially used tickets and the refund almost no one claims
If you board a train and have to break your journey mid-route, a family emergency, an illness, you are entitled to a refund on the untravelled portion. This requires surrendering the ticket at the station where you detrain and obtaining a certificate from the station master. The refund is calculated on the fare for the distance not covered, minus a cancellation charge. Almost no one does this because the process requires finding the station master's office under duress. It is, however, a legitimate entitlement under the Indian Railways Refund Rules, 2015, and on longer routes the unclaimed amount can be significant. The certificate must be obtained before you leave the station, there is no retrospective version of this claim.
The RAC ticket and what you are owed if the berth never materialises
A Reservation Against Cancellation ticket entitles you to travel, sharing a side berth, but not to a full berth. If you travel on an RAC ticket and the berth never upgrades to confirmed during the journey, you are entitled to a refund of the difference between what you paid and the fare for the class you actually occupied. This is not automatic. You must apply at the destination station before leaving the premises, with the ticket and a written request. The refund is processed by the commercial department of the originating zone. Very few passengers know the entitlement exists; fewer still stay back at the destination station to file it.