I just went through and calculated all of my cycle lengths for the last year and it's anywhere from 28-38 days. Glow says it goes off the length of your first cycle recorded, which probably makes it very inaccurate. I'm on cycle day 33 and glow says I'm 4 days late on my period, but I've had 4 negative pregnancy tests. So frustrated! I'm guessing I just need to take an ovulation test every day next cycle to even know!?