Confused about fertile window/Ov

Okay..I have a few different apps..and glow has now switched my period because its a few days late..which is fine. Well it also moved my fertile window and the day I'm assuming I'd ovulate too..so it doesn't match last months dates. My other app has not switched any of those dates when I entered a late period. So..which is right? Would it be the same as last months or different? Wouldn't it be roughly 14 days or so after whenever my period starts? Anyone know..?