Due Dates and Trimesters

Due dates and trimesters. Your doctor will help you determine your expected due date at your first prenatal visit. Your due date is 40 weeks from the first day of your last period. It’s important to remember that your due date is only an estimate – most babies are born between 38 and 42 weeks from the first day of their mom’s last period, and only a small percentage of women actually deliver on their due date. 

Another term you’ll hear throughout your pregnancy is trimester. A pregnancy is divided into trimesters:

  • First trimester is from week 1 to the end of week 12 (months 1–3).
  • Second trimester is from week 13 to the end of week 28 (months 4–7).
  • Third trimester is from week 29 to your delivery (month 8–delivery).
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