Pregnancy Due Date Calculator
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Pregnancy dating guides

Short, sourced explanations of the questions behind every due date.

  1. How due dates are calculatedNaegele’s rule, cycle adjustment, conception, IVF and ultrasound, each with a worked example.
  2. How accurate is a due date?What studies show about birth timing, and why the date still matters.
  3. Ultrasound vs last periodWhy the dates differ, and the thresholds clinicians use to change them.
  4. Weeks, months and trimestersCompleted weeks, trimester boundaries and a weeks-to-months table.
  5. What does full term mean?Early, full, late and postterm in exact weeks and days.