Ovulate before or after the “halfway” of your cycle?

Do you ovulate before or after the “halfway” day mark of your cycle?

I have about a 30 day cycle on average, and my apps have been suggesting I ovulate around cycle day 16 or 17. So, I’ve been starting my OPKs around day 13 or 14. I’ve never gotten a really strong positive, but my testing isn’t always the most consistent so I blamed it on that. But I’m on month 7 of trying, so I figured why not start testing a little earlier. What do you know, it’s cycle day 11 and I got a strong positive opk. Not just a matching line, a test line darker than control line kind of line.

Is this normal? That I could ovulate so far ahead of my “halfway” mark? I’m a full 6 days before Glow thinks I’d ovulate and 4 days before PreMom, but it’s the strongest opk I’ve ever had by far.

Thoughts?

Thank you all!!