This is my first month using OPK's. My husband and I have been ttc for about 4 months by just using glow and trying not to stress. This month I decided to use OPK's to see how close glow was to my actual ovulation because I've been worried I'm missing my window. SO Glow says that today is the last day of my fertile window, 7.6% chance but this was my OPK this morning. So I think glow is a few days off, so I'm glad I checked!