Note the first day of your last menstrual period (LMP)
Count 40 weeks from the first day of the LMP to estimate the due date
Count 280 days from the first day of the LMP to estimate the due date
Use the first day of the LMP to calculate the current gestational age in weeks and days
If you know the conception date, count 38 weeks or 266 days from that date
Use an ultrasound date and measurement if the LMP is unknown or cycles are irregular
Compare the estimated due date with the current date to determine how far along the pregnancy is
Confirm the calculation with a healthcare professional if needed