Different AF dates

Kellie • Mother of three and currently ttc #4 due to health issues my chances are starting to shorten every day! Staying positive and wishing everyone lots of baby dust
I have two different fertility apps that I use just to see the difference... One app (fertility friend) says AF was due on the 6th and glows app says Sunday AF is due.. I'm confused! Does anyone else use a different app as well and it's a big gap in the time frame AF is suppose to be due!