hi! i myself not sure how to calculate hw many weeks im in 😅 based on our LMP, theres usually a calculator online to help give a rough estimation of how many weeks we are. from my personal exp, so far the estimation has always been about the same as to when i went for my first gynae checkup. https://www.whattoexpect.com/due-date-calculator/
Still use LMP to calculate number of weeks. Anyways that one is not accurate. Based on gynae first scan is more accurate.