App dates off?

Amanda • Married for five years to my best friend, and Mom of one boy, and new baby girl born 7/15/16
According to another app I use, I should be 3w 3D, but on Glow I am 2w 6d. My LMP was October 27th. Why are they different? I know the 1-2 on the clearblue is dated as 3-4 by the Doctors.