How is my due date calculated?

Your due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (assuming a 28 day cycle).

Note that your menstrual period and ovulation are counted as the first two weeks of pregnancy. If you deliver on your due date, your baby is actually only 38 weeks old, not 40.

What is Ovulation?

Ovulation is one part of the female menstrual cycle whereby a mature ovarian follicle (part of the ovary) discharges an egg (also known as an ovum, oocyte, or female gamete). It is during this process that the egg travels down the fallopian tube where it may be met by a sperm and become fertilized.

Early Signs of Pregnancy:

  1. Absent menstrual periods (amenorrhea)
  2. Nausea and/or vomiting (morning sickness)
  3. Unexplained fatigue
  4. Frequent urination
  5. Breast tenderness and changes
  6. Excessive salivation (ptyalism)
  7. Headaches
  8. Backaches


Please remember that your due date is only an estimate. On average only 5% of births take place exactly on the estimated due date. Most are born within a week either side of the estimated due date.
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