Calculating due date

I am getting conflicting due dates, I think because my menstrual cycles are shorter than average (24 days).

I ovulate around day 10.... LMP was June 10, and had timed intercourse June 16 and 19, which means implantation happened by June 20 or so.

If I use June 20 conception date, I’m 6 weeks. If I use June 10 LMP, I’m 5 weeks, 4 days.

Any ideas which one is more accurate??

I’m 40 years old and looking at statistical probability of miscarriage. It dies down every day, so if I’m further along, I’m safer! But I don’t want to give myself false hope.