Fertile window confusion!

Hi lovely ladies.  Is anyone else frustrated about your fertile window predictions?  I have 3 apps on my phone....all have the same period data, but one says my fertile window begins the 7th, the other says the 8th, and Glow says 11th!!  I will keep track of my CM, but it is just frustrating that I have 3 different predictions.  Not sure which one is accurate.  Sorry, just venting I guess.  Will just keep trying to enjoy the journey and hope we receive our positive soon!!