“How do I figure out my due date?”
Doctors date your pregnancy from the first day of your last menstrual period. You’ll probably soon have the date memorized as every time you visit your doctor or another medical professional, they will ask you for this date. A normal pregnancy lasts 40 weeks from the date of your last menstrual period, although anything within 3 weeks of that mark is considered “term” (normal). When we talk about your pregnancy as being so many weeks along, we are using this date for our calculations.
Here’s a rough calculation of your expected due date: add 9 months and 1 week to the date of your last menstrual period. Not too much rocket science, but you now have your approximate due date.
As your pregnancy progresses, your doctor or midwife will have a better sense of your due date based on their examinations and measurements, aided greatly by your ultrasound at 18-20 weeks, during which the technician will also take detailed measurements. Your doctor or midwife may revise your estimated due date after receiving your ultrasound results.