Count pregnancy from the first day of your last menstrual period
Use that date as pregnancy week 0
Add 7 days for each completed week
Pregnancy is usually measured in weeks and days
A full-term pregnancy is about 40 weeks from the last menstrual period
If you know your conception date, pregnancy is about 38 weeks from conception
Use an ultrasound date if your last period is unknown or irregular
Ask a healthcare provider to confirm your due date if needed