I'm due October 11. According to the calculator online it says that my last period was Jan. 5, which can't be since I had sex on Jan. 6. I don't remember my last period because it was irregular, sometimes it was the beginning of the month then it would change to the end of the month. My problem is that I had a one night thing (my first and last) with someone on Jan. 6 and I'm concerned that there is a possibility of him being the father. My doctor says the ultrasound is very accurate, give or take 7 days. I seem to be measuring good at every appointment, so the babys size seems to be on target. Also, I've read that sperm can live inside a woman under the right conditions up to 7 days, which probably isn't likely but could be possible. Given this info, do you think there's a good chance that the individual I had sex with on Jan. 6 is likely the father?

I had sex with someone else that month also, I don't remember the exact dates now since it was so long ago but it was more than once. I was wondering based off the due date and that date of intercourse on Jan. 6, how likely it would be that its that mans baby?