Period apps giving me different AF dates


The first app “flow” says AF Is due in 3 days

The second app “Premom” says AF due in 1 day

The third app “fertility friend” says AF due in 2 days.

Why is this? I log my periods and ovulation every month into each of these apps and they never have the same expected period date. I’m 12 dpo and had some spotting last night and this morning. It would be nice if they were all telling me the same thing.