Lol it's not October and May. Everyone gets paid at different times of the week. Some get paid on Thursdays, some Fridays, etc. Also, different weeks, maybe we're both Fridays but your pay is this week and mine is next week, that'll change the months that get the 3rd paycheck. Also, every year it changes too, not always consistent. The only month you know it probably won't be would be February. Unless it perfectly works out that when a pay occurs on Feb 1st, it's also a leap year.