Late spring through early autumn is the easy answer — May, June, and September are the most pleasant. July and August can be hot, with temperatures in the low thirties, though Szombathely's leafy parks help.
The city's biggest event is the Savaria Historical Carnival, held in late August. It is one of Hungary's largest historical reenactments, with Roman legions, gladiator fights, and a parade through the old town — worth timing a trip around. The Bartók Festival, in July, brings classical concerts to the synagogue concert hall.
Winters are grey and cold but rarely brutal, and museum prices stay the same.