Prague Castle Ticket, buy online or on the day?

I’ve been there twice and just bought admission at the ticket office which is in the castle courtyard. There might be a wait of 5-10 minutes which lets you soak in just how enormous St. Vitus Cathedral is.

Buy on the day but price is the same. Use the ticket office in the third courtyard opposite the entry to the cathedral. SInce 1st March 2024 the price has increased from CZK250 to CZK450 for adults reduced to CZK300 for people who have had their 65th birthday. Ticket is valid on the day of purchase and the following day. No timeslot is required, just turn up.

Thanks, will just buy on the day. I plan on taking Tram 22 uphill instead of walking, will the ticket office be near there?

From the tram stop walk across the road, over the bridge and through the first passage into the Castle buildings (that's the 2nd courtyard). Turn left into the passage until you have the doors of ST Vitus in front of you (that's the 3rd courtyard). The ticket office will be behind on your right. 3-4 minute walk. Just pick a desk to queue for a few minutes. If everything is heaving then try the ticket office next to the entry of Golden Lane which sells tickets but not the audioguides. If you are claiming the senior discount have your passport ready.
I asked at the castle why ticketportal has a time slot allocation and was told that initially it's just to see what the busy periods are but at some point in the future in order to control numbers they may go to a pre-booked slot system where you pay in advance and show a QR code for entry at a precise time.

Alright thanks , I've seen the ticket office on google street view. What time would you recommend we go? Early in the morning right after it opens?

Ticket office and buildings open at 9am but it's nice to walk around the courtyards earlier when it's quiet. Arrive early as possible and allow some time to get to the main entry at 12pm to see the changing of the guard.