I need some help figuring out dates of my pregnancy to determine who the father is?

Calculate: Early dating based on last menstrual period is not specific enough to be sure of a conception date. If you get an ultrasound, it will likely provide better data & come up with a revised due date. If you look back 1yr from a due date & add 12wks you will have projected conception date. If there is any overlap in exposure around the dates, dna testing may be needed.