Opk test and cycle days

So i started testing my ovulation yesterday (CD 5), and i was expecting kind of what the result was on CD5 last cycle so barely a line (i knew it was going to be negative, but i wanted to have the line progression) .. to my surprise, it was more close to what my result was on like CD12 on my previous cycle, and today CD6 closer to CD15.. Maybe i will ovulate closer this month?

So i was wondering for those of you that have more experience with opks, do you ovulate around the same cycle days every month or not really?