I had implantation bleeding on aug 25th. i countback conceived aug 15th. ultrasound due date may 1st could i still conceive on15th with that duedate?

Possible...: If we use that due date the conception date would be August 8th, however if the due date is determined by an US this is usually off for a few days so it is possible a close alternative day could've been the conception date. In other words it may vary esp. if your periods are not usually regular.

Conception: A May 1st due date would correlate (assuming 28 day cycle). actually would be more likely around August 8th. LMP of 7/25 give's due date of 5/1. Perfect 28 day cycle ovulation would be around 14 days after 7/25. But all this is approximation. Implantation bleeding often times does occur around the time of expected LMP, so 8/25 makes sense. 1st trimester US is accurate within 5-7 days though