They go by your last period so your 5 weeks.
Your EDD is 40 weeks from the first day of your last menstrual period (LMP). If you deliver on your EDD, your baby is actually only about 38 weeks old — that's because your egg didn't become fertilized until about 2 weeks after the start of your last menstrual period.
I agree completely with cch1029 so technically baby is 3 weeks but overall your pregnancy is 5 weeks when you add the period in
Your due the same date as me. I have an early pregnancy scan on Monday xxx