Ovulation help!!??

Tabatha
So my cycle is usually always 27 days and I've always been told to count the first day of my period as cd1 and on cd14 should be your most fertile day, but glow says different. Glow says my most fertile day is the 18th. I'm still new to all of this; DH and I are trying to conceive baby #1 going on 3 months now