My monthly cycles run 26 days, my last cycle was 3-15-2009. I had a one night stand on 3-22-09 I don't think he ejaculated in me but I'm not 100% certain. I had sex with my boyfriend on 3-28-09 I ovulated on the 28th or 29th. I missed my period on 4-13-09 took an ept test, the results were positive but a very faint line. My question is this: Since sperm can live from 3-7 days what day was the day I most likely conceived on ? The 22nd or the 28th? What would a leutial phase be for someone with 26 day cycles? Is a ultrasound for size dating more accurate than going by an ovulation calendar?

... did you just cheat on your boyfriend?

To be honest, using a calendar to figure out the paternity of the child won't really hold up too well...

I suggest you come clean, and get a paternity test.

I hope you know doctors ESTIMATE how old the fetus is.

Sarah

I believe your question was already answered here...

https://www.askmehelpdesk.com/womens-health/conception-dates-345331.html