is there any rhyme or reason to the layout of final exams?

i’m trying to plan a vacation in late December and there’s a deal on flights on December 18th. I know I technically could still have an exam that day though, but the prices just increase every day and I don’t necessarily want to wait until mid-October to book a flight. is there any standard schedule they follow for the exam schedule (intro/bigger classes vs more specialized classes first/last)? or is it just a gamble every year?