I've seen soooo many women (mainly those who don't use OPKs) base everything off of glows predictions. Well, I'm speaking from experience... GLOW CAN BE WRONG! If you're on your fertile week but OPKs are negative, glow is wrong! If you are solely basing your BD'ing off of glows percentages, without OPKs, YOU AND GLOW might be wrong. I know because my 2nd month on glow (first month was trial and error) glow said I was in my fertile week so I tested with OPKs and they were all negative. Come to find out, a few weeks later, I was already pregnant because I OVULATED BEFORE GLOW ASSUMED I WOULD. So please ladies...use OPKs to confirm whether glow is right or wrong...and to be safe, start using OPKs right after AF is gone!! Your fertile week may be before glow says...and if you don't BD or use OPKs regardless of what "week" you're in...your chances of being out that month increases!