Third Day?

I’m new to the forum, but was hoping someone could refresh my memory. It’s been over 6 years since I had to take fertility meds (specifically, Clomid) and it says take between days 3-7 of cycle. Well, do you consider the first day to be when you began spotting (which is usually old blood) or do you consider it the first day of a full flow?

First day any blood I count as day one .