Why does the internet say ovulation happens 12 to 14 days before your next period and, or by subtracting 14 from the number of days in your cycle (for ex. 28 - 14= 14). Meaning ovulation will occur 14 days after my period. When I calculate one or the other I get a different ovulation date from Glow/or this app. I started my ovulation kit yesterday and I have been positive yesterday and today but Glow shows my ovulation day to be today. But, when I subtract 14 from my normal cycle days it says ovulation day will occur on the 8th and then when I count 14 days before my next period I am suppose to ovulate on the 4th. What do I do and which is accurate to f