When did i conceive. To be july 16?

Dear Ma'am, Thank you for your query regarding date of conception. While calculating the estimated date of delivery or EDD,  there are two things that you need to consider. 1. Date of last menstrual period. (LMP) 2. Date of conception when embryo transfer in IVF is done. For all intents and purposes the date of conception is not considered important when calculating the estimated date of delivery. It is possible to conceive with one unprotected act, but it is rare. The first act you have described is within first 7 days of period,  where fertility is less. There is a possibility of you being pregnant with the pre-ejaculate of the act on the 25 th October. Your EDD by naegles formula if LMP is 9.10.2016 is 16.07.2017. Please note, the last period is the first day of the period and not the last day of bleed. If your due date with first trimester ultrasound is within 7 days of your calculated due date with LMP.  The LMP date is given predesecence. I hope I was able to resolve your query. Regards, Dr. Aditi Kishore Shinde