cycle day 1?

So last night I started my period. It was about 9 pm and was light to medium. Just some red blood when I wiped. This morning I woke up to my normal flow. My question is, what should I consider CD1? Yesterday or today? I'm taking femara CD3-7 and will get an <a href="">iui</a> when I ovulate so I don't want to mess that up. Thank you for any advice!!