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Full flow counts as cd1.
As far as luteal phase, I have 2 phone apps.
1 says my cycle is 28 days, the other 27. So I am thinking that you pick one or the other, and stick with it. Anything under 10 days is supposedly possible luteal defect, according to google results, but your RE/DR would know best.

My first day of my cycles always started with a lil bit of brown discharge for about 1 hour then full of flow. It can be diffrent for every person but I agree with littleclay its usually full flow that counts as day 1

Hi Michelle! My doc recently told me any spotting that develops into AF is CD1. Luteal phase is calculated from the day after O (day of temp rise) up until the day before AF. And I guess your own LP depends on what you want to consider AF. If you wait until full flow to call it CD1 then the spotting would be your previous cycle giving a day or two longer LP. But my thought is that if I'm having spotting around 13 or 14 dpo I'm prob not pg and I might as well move on to a new cycle. Hope this helps.