When am I ovulating? Help please

fayre
I have a 28 day cycle as I'm on a 21 day pill and a 7 day break between the next pack.. 
So I can work out when I am ovulating, when is the first day of my cycle? Is it the first day of my period? Or first day after finishing my period (when I go back on my pill for the month)
I know some pills actually stop ovulation but I would still like to know when my fertile window would be.