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well when you say over night depends what time you mean, if you started bleeding (red Blood) say monday 5pm then thats the star, if it was 8 hours later at 1am then it would be Tuesday. if that makes sense

If u wake up to a period then cd1 is the day u woke up. U cant pinpoint when it started unless u woke up at 11:59pm and it was there, in which case, cd1 would be that current day before the calendar date change.

My doctor counts day 1 as full flow before 5:00pm. So when you wake up, it's CD1.

I don't get that. Why does your period have to start before 5pm?? Mine usually comes around early evening most times. I count that as CD1. Surely as long as it's full flow which mine always is then shouldnt it be classed as day one of your cycle?! Just curious!!