Why my conception date wrong from my due date my conception date is july 23 but i had sex july 25?

Conception can occur up to 6 days after sex, so this could be explained by an earlier sexual encounter (as early as July 17). If your due date was calculated from your LMP then this could occur when you have slightly longer cycles from the typical 28 days. If your due date was derived from an ultrasound there is simply imprecision in the measurements and subsequent calculation.