I started using glow a couple months ago and when it asked how long my cycles were I put 32. Then a few weeks after I started I put all my period in for the last 6 months. They jump around a bit from 26/28 then sometimes it's 32 days. Now it notifies me on my fertile day Feb/4 which is correct. My peakday was February 8 at 33%, but the Notification came on February 12 at 3%.