When is your ovulation day

Based on a 28 day cycle what is the most common day to ovulate? I’m on letrozole which puts me on a 28 day cycle. I’m currently going to do my second round of IUI, and go for my 12day ultrasound tomorrow. Last month when we did IUI things got confusing with my trigger shot. It was shipped on the correct day and I ended up giving myself the trigger shot on the same day IUI was done, is that normal? I’ve read so much that people have done it one to two days before IUI.