I started my period 23rd of July 2011 I cheated on my husband 6 of Aug 2011 we are working through it I took a pregnancy test Aug 20th and found out I was pregnant I went to the doctor Nov.29 for a sono I was 18 weeks and 4 day who is the farther and what date would you is my conception

Sorry to say but the ONLY sure way to find out who the father is would be a DNA test AFTER the birth.
It's NOT possible to accurately work out the conception date, it's all best guess.

Agreed, the 18 week 4 day is a guess, it is give or take a week or at times even two weeks. It is based on average sizes of fetus at certain ages, plus info you gave them of your last period.
So it could be either men, at this point, you will have to get a DNA test when the child is born. I am sorry we could not resolve the issue for you.

Remember that all of pregnancy is guess work. We go by your LMP, which was 7/23. That gives you an approximate (remember it's just a guess since we don't know EXACTLY when you ovulated) conception date of 8/6.

I was using the wheel that the OB/GYNs use to calculate due dates. This wheel also gives us an approximate conception date.

In the end, you will have to have a DNA test to determine paternity.

This is the wheel I am speaking of. http://www.imprintitems.com/sitewide/images/prod/0_healthcare_charts_-_cards_-_calculators_20_-_gestation_-_calculator_lg.jpg