how accurate is you period tracker?

Just curious how on/off this tracker is for everyone. I just got off the pill in June and for the first two months it was dead on then the next month I was 3 days off no big deal and no I'm on day 6 being late. Just curious if I should think anything of it lol FYI I tested a week ago cause I thought I could be but nothing that's why I'm asking everyone else's experience.