Help Choosing CD1

Camille

So the past few months I tend to spot 2/3 days before the full force of AF arrives. So I spot during a day, then a nothing for 2 days, and then AF arrives. Do I take my CD1 from the spotting or from full force AF? I am monitoring my bbt now for the first time this last month, and it dropped this morning, but I have been spotting on and off since Saturday.... No BPF and not expecting it. Patiently waiting for full force AF.