When do you officially count your period starting?

So I always start my period every 28 days.. and I usually have a 4 day period. When I first start I always have brown discharge but no blood in my pad.. When I use the restroom I always pee clots and when I wipe it’s red. And on the second day I usually have a heavy flow. Is the first day I had clots and brown discharge when I officially start my period? Or is it the second day when I have a heavy flow? I need help this is fairly important so I can track my cycles right. So If the brown discharge is my official start date then it would be a 27 day cycle