PREGNANCY DUE DATE CALCULATOR Create your personal pregnancy timeline   Enter the first day of your last menstrual period and click "Calculate": Month: January February March April May June July August September October November December Day: Year: Your Conception Date is: (Approximately two weeks after your last menstrual period) You're in your First Trimester (weeks 1-12) Your period of greatest risk for birth defects is:   (Five to ten weeks gestational age)      to Your baby's fetal organ formation begins Your baby's major organs have formed: Your risk of miscarriage decreases: (weeks 12-27) If your baby is premature, but born after this date, s/he has a chance to survive: Your Third Trimester begins on: (27 weeks) Your Due Date is: (40 weeks - full term)