If my ultrasound matches lmp, when would i most likely have conceived?

2 weeks after LMP: Because the ultrasound dating estimate presumes 28-day cycles and ovulation at mid-cycle, when the LMP matches the ultrasound dating estimate, one can presume that conception occurred 2 weeks after the LMP. That means 2 weeks (plus or minus a few days) after the first day of the LMP. In reality, there is no way of knowing exactly when conception happened (in a natural, non-IVF, pregnancy).