How many weeks am I?

Vik

Help! My last period started at May 16. I have irregular cycles but they usually go to about 35-40 days. I think this one was 40 days. How many weeks am I? Do I still go by the first day of my last cycle? How accurate is that for people with 40 day cycles? First doctor appointment isn’t until 4 weeks from now. Any comments will help! :)