Questionsssss! I am TTC.

Hey guys! Okay, so I started my period yesterday on the 11th. Should I start taking ovulation tests on the last day of my period?? Or should I wait a day or two after my period ends before taking a ovulation test?? I don't want to miss my little window of opportunity this month, therefore I want to track my cycle as carefully as possible and be sure of when I am ovulating. But ovulation tests are EXPENSIVE! I was going to go buy a few of them sometime this week so that when I do get off my period I will have them. But I don't want to waste any of them and have to go buy more just because I was so anxious to test! Any and all advice is welcome