When was your last period if due date is august 9th?

To calculate when your last period was if your due date is August 9th, you need to subtract 280 days from August 9th. Since a standard pregnancy is 40 weeks or 280 days, this will give you the approximate date of your last menstrual period (LMP).

So, counting back from August 9th, your LMP would be around October 18th.