Which ovulation app is correct?

[Crazymummyto3]

I logged details of my periods, when I've had positive OPKs last month etc into two different apps and got two different fertile windows! How can I tell which is the end one to go from?? Is it always 14 days from ovulation to AF? I never charted my cycle in any of my other pregnancies, I think my age has made me more aware of it this time!

The apps are just a guide, don't follow them exactly. Your body will tell you are ovulating, DTD every other day around your fertile window and on ovulation day if you can x