How accurate are these predictions for ovulation since they’re all different? Just out of curiosity. I started tracking with OPKS yesterday and no surge yet. Last period July 6 for 5 days last cycle 35 days. It’s different every month.

My last period started on July 6, it lasts for 5 days and my last cycle 35 days. I’m irregular, I’m seeing a doctor and I started tracking yesterday with OPKS. No surge yet. Not sure if I missed it or haven’t gotten there yet. Just out of curiosity which date on these would be more accurate since they’re all different?