How do they come up with these dates!?

[Whulfc86]

I'm pretty sure I know the date of conception to be Nov 20th, calculators are saying I'm 6 weeks + 1 day, how is that possible!?

It’s calculated from your last period

Because they count from the first day of your last period not from conception. If you did conceive on 20 November then that would be approx day 14 of your cycle (ovulation is day 14 of a 28 day cycle) I.e you’re already counted as being 2 weeks pregnant at the time of ovulation so the calculators are right in your are 6+1

• the calculators are right in saying you are 6+1

Oh yes I know the calculatior is right I was just wondering how. Thanks!