I’m confused

Kristenemerson

My period was July 21 lasted for five days it was due August 13 but came on August 16 I’m try to count the days correct to get my ovulation right because I’m trying to convince a baby but I don’t know if I’m counting right maybe somebody can help me so I can fix this I start taking fertilaid tomorrow an I half to take it three times a day can somebody help me count this to get it correct