Use the first day of your last menstrual period (LMP) as the starting point
Count the number of days from the LMP to today
Divide the total days by 7 to get the number of weeks pregnant
Use the remainder days to estimate the extra days beyond the full weeks
If you know the conception date, count from that date and add 2 weeks
If you have an ultrasound date, use the gestational age given by the ultrasound
Compare your result with a pregnancy calculator or healthcare provider for confirmation