It’s also not an exact science, especially if you’re not on hormonal birth control. My cycle is 27-29 days, unless I’m stressed, in which case it can be up to 40 days. My period then lasts 3-4 days, but every 7-8 months, it instead lasts a full week and is way, way heavier and more painful than normal. No medical issues that my doctor can tell, sometimes it just be like that. So I will know that I should be getting my period in the next couple of days, but it’s never exact.

I used to be better about tracking it, but I realized I could feel a twinge about 20 minutes before the bleeding starts. Now I’ll even wake up to it, so there’s really not a downside to not tracking my period. (Except unforeseen medical issues, bc failures, and general bodily awareness)