Are some girls REALLY that regular!?

I see posts all the time saying "my period was due on the 4th it's now the 5th I'm a day late what do I do!??" 
Even when I tack my period it is NEVER that regular down to the day lol. Sometimes the 11th maybe the 13th, some months the 16th... Just always around the middle of the month lol. 
How would you ladies describe your period: super dependable and always on time, or do you just estimate when it will arrive (and not flip out if it's "late") like me!?