Calculate pregnancy ?

Adina • I`m 24 with a 2 year old boy and another on the way. Married for 3 yrs.

So many calculators say 5 wks, 4 wks, or seven. How do I calculate ? It’s too early for an appt. I’ve already contacted my doctor. I usually have a 4 day long period which comes at the end of the month. My last period was March 22-26.