Hang on, let me count again
For the 13th I make it the 27th March, give or take a few days...
But the pp's are right, you'd not show on a pregnancy test that early if it was the other guy.
I was 15 days past conception before I got a positive.
I counted backwards 38 weeks would be estimated conception it can be a few days either way though.
(+ an extra 2 weeks would be previous estimated period dates.)
Most probable conception date: Mar 17, 2016 - Mar 21, 2016
Most probable sexual intercourse date that lead to the pregnancy: Mar 14, 2016 - Mar 21, 2016
Possible conception date: Mar 16, 2016 - Mar 26, 2016
Possible sexual intercourse date that led to the pregnancy: Mar 11, 2016 - Mar 26, 2016
Most probable conception date: Mar 22, 2016 - Mar 26, 2016
Most probable sexual intercourse date that lead to the pregnancy: Mar 19, 2016 - Mar 26, 2016
Possible conception date: Mar 21, 2016 - Mar 31, 2016
Possible sexual intercourse date that led to the pregnancy: Mar 16, 2016 - Mar 31, 2016