When is first official day of AF?

So AF came late evening this month. It wasn't full bleeding until next day, but it was spotting that got heavier every time I wiped. And now 5 days later Im spotting brown meaning Im almost done. Tomorrow will be clear. My question is, Do I count first day with spotting or heavy bleeding? Because if I count spot day including today that would mean I've been on AF for 6 days. And that would mean O day would get pushed back.