Where are you departing from?
If your station has a ticket office or ticket vending machine, then you must buy your ticket before you board the train. If you are departing from a smaller station that does not have these facilities, you can buy your ticket aboard the train from the guard. Find out how to look up which facilities are available at your station.
What kind of trip are you taking?
For shorter trips (for example Exeter to Barnstaple), you can buy tickets on the day – there is no cost saving if you book in advance.
If you are travelling longer distances, to get the best price you should buy your ticket in advance. Tickets can be bought up to 12 weeks in advance and the earlier you can book, the cheaper it will be. Buying a ticket for a long distance journey on the day will mean paying the walk up fare which can be very expensive.