has anyone used two different apps and gotten different fertile window and ovulation dates?🤷‍♀️

Amber
i had used glow put in this info and have even counted from one period to the next to be exactly sure my calculations are right. 
40day cycles lasting for 6-7 days
glo app: on top. suggest my fertile window to be all at the end of march not the start of
april.
ovulation predictor: on bottom of photo, suggests march and thru april.