Due Date Calculator
Estimate your due date from your last menstrual period or conception date, plus your current gestational age and the key dates along the way.
Assumes a typical 28-day cycle with ovulation around day 14.
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Where today falls on the timeline
The bar shows how far today sits between the last menstrual period and the estimated due date, out of the full 40-week timeline.
How a due date is estimated
The standard method — Naegele's rule — adds 280 days (40 weeks) to the first day of the last menstrual period. It assumes a typical 28-day cycle with ovulation on day 14, so it's a population average rather than a measurement specific to this pregnancy.
The conception-date method is the same 280-day estimate counted from a different starting point: 266 days from conception (roughly ovulation) rather than 280 days from the last period. In a standard 28-day cycle the two methods land on the same date, since conception typically falls 14 days after the last period began.
The method
Conception method: due date = conception date + 266 days
Worked example
A last menstrual period starting January 1 gives an estimated due date of October 8 — 280 days later. Estimated conception, 14 days after the last period, falls around January 15; adding 266 days from that date lands on the same October 8 due date.
Frequently asked questions
How is a due date calculated from the last menstrual period?
Why is the conception-date method different from the LMP method?
What are the pregnancy trimesters and milestone dates?
How accurate is a due-date estimate?
- Naegele's rule (LMP + 280 days) — long-standing obstetric convention, described in ACOG (American College of Obstetricians and Gynecologists) patient guidance on estimating due dates.
- Trimester boundaries and full-term range (37–42 weeks) — ACOG Committee Opinion on definition of term pregnancy; viability commonly cited around 24 weeks per general published perinatal medicine guidance.