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Pregnancy Due Date Calculator

Calculate your estimated due date from your last menstrual period or conception date, with a week-by-week pregnancy timeline. Free, instant.

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Understanding your estimated due date

The estimated due date (EDD) is the date by which your baby is expected to arrive — exactly 40 weeks from the first day of your last menstrual period. It is a statistical midpoint, not a precise prediction. Knowing your EDD helps you plan antenatal appointments, prepare for maternity leave, and understand how your pregnancy is progressing. The American College of Obstetricians and Gynecologists (ACOG) outlines the recommended methods for estimating gestational age and due date, including LMP-based dating (Naegele's rule) and first-trimester ultrasound.

Pregnancy week-by-week milestones

  • Week 6: Heartbeat detectable on transvaginal ultrasound.
  • Week 12: End of the first trimester. Nuchal translucency scan and early anomaly screening.
  • Week 18–20: Anatomy scan (anomaly scan) — checks all major organ systems and confirms gender if desired.
  • Week 24: Viability threshold — babies born after this point have a chance of survival with intensive care.
  • Week 28: Third trimester begins. Glucose tolerance test (GTT) for gestational diabetes.
  • Week 37: Early-term. Baby is considered ready for birth but benefits from remaining in the womb until 39 weeks.

Important note

This calculator is for informational purposes only. Always consult your obstetrician or midwife for accurate pregnancy dating and personalised prenatal care. Ultrasound dating in the first trimester is more accurate than LMP-based calculation if your cycles are irregular.

How cycle length affects your due date

The standard Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer — say 35 days — ovulation likely occurs around day 21, making your conception date about 7 days later than the formula assumes. This means your EDD should be shifted forward by approximately 7 days. Many obstetricians adjust the LMP-based EDD based on your reported cycle length or early ultrasound measurements.

For IVF pregnancies, the due date is more precise because the exact fertilisation date is known. A Day-5 blastocyst transfer date is equivalent to day 19 of a standard 28-day cycle, so the EDD is calculated as transfer date plus 261 days. This removes the ambiguity of natural conception dating entirely.

Frequently asked questions

How is the due date calculated from LMP?
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. The formula: EDD = LMP + 9 months + 7 days, or simply LMP + 280 days.
How accurate is the calculated due date?
Only about 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the EDD. An ultrasound scan between 8–14 weeks provides a more accurate dating than LMP, especially if your cycles are irregular. Your doctor may adjust your due date based on the scan.
What are the three trimesters?
1st trimester: weeks 1–12 (LMP to 12 weeks). 2nd trimester: weeks 13–26. 3rd trimester: weeks 27–40. The 1st trimester is the period of highest miscarriage risk and critical organ development. The 2nd is often the most comfortable. The 3rd involves rapid baby growth and preparation for birth.
What does 'full term' mean?
A pregnancy is considered full term between 39 weeks 0 days and 40 weeks 6 days. Early term is 37–38 weeks; late term is 41 weeks; post-term is 42+ weeks. Babies born before 37 weeks are preterm. The safe delivery window (37–42 weeks) is 5 weeks wide, which is why the due date is an estimate, not a deadline.
How is the due date calculated for IVF?
For a Day-3 embryo transfer, add 263 days to the transfer date (LMP is calculated as the transfer date minus 17 days). For a Day-5 blastocyst transfer, add 261 days. IVF due dates are more precise since the exact fertilisation date is known.

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