Even if you count yourself using whatever method, and when you go for your first appt, they’ll do the math for you. I thought I was 7 weeks when I went for my first appt, turned out I was only 5 weeks and lucky me, I could see the heart beating. So I counted from their calculation and upon 2nd appt at 10 weeks 2 days turned out I was supposed to be 10 weeks 7 days which means the following day I was supposed to be 11 weeks already. So I’d say don’t put so much thought about how many weeks it is, give or take 1 or 2 weeks plus minus from the first day of your LMP.
Count from first day of last menses. But when u go hospital they will count again. Sometimes the date might be different
There are online pregnancy calculators you can try.
Start counting from the start of your last menses