From the Planner tab, when doing a search that shows prices, you can add your railcard in the Passengers section.
Note that you can only add one type of railcard. So if you are buying tickets for multiple people, it may be necessary to travel with multiple railcards.
If you’ve set more than one passenger, the message here will let you know how many railcards you’ll need.
The railcard icon
This icon lets you know if a railcard discount has been applied. Railcard discounts are applied in addition to Split Ticket savings.