Confused about Fertility/Ovulation

Okay so last month August (I had my period from the 13th-17th) I ovulated on the 28th - Only reason I know that is because I took a ClearBlue Digital Ovulation test that had a smiley face. So that is about 11 days after my period. How come the app this month is saying this? I'm confused? When am I in my fertile window? Thank you in advance!