Okay to calculate your due date:
1. Figure out the FIRST day of your last menstrual period
2. Add seven days to that date (for example: My last period was June 3 so this would give the date June 10.)
3. Add 9 months to this date (So this would be March 10)
This is only approximate as I actually gave birth March 14 but only 5% of girls actually have the baby on their due date.
To figure out your gestational age (how far along you are):
1. Figure out the FIRST day of your last menstrual period
2. Look at which day of the week it was on (ex: Monday)
3. So if it was on a Monday then every Monday after that you would add 1 week to your gestational age. So two weeks after your period started you’d be two weeks pregnant. The doctors use this to formula to make a 40 week pregnancy calendar even though this means you were technically pregnant for TWO WEEKS before you conceived. An actual pregnancy is 38 weeks. If you subtract two weeks from your gestational age as calculated above you have your FERTILIZATION AGE which is the actual amount of time you’ve been pregnant.
Please remember that this is not exact and that is why ultrasound dating is helpful also.
Best of luck.
Sara