Pregnancy Due Date Calculator
Estimate a due date and gestational age from the last period.
A rough estimate based on a regular cycle — not medical advice. Most babies arrive within a couple of weeks of the date, and an early ultrasound dates more accurately. Always follow your midwife or doctor’s guidance.
How the date is worked out
Pregnancy is dated from the first day of the last menstrual period, not from conception, because that day is easier to know. The widely used Naegele’s rule adds about 280 days — forty weeks — to reach the estimated due date.
due date ≈ last period + 280 days (± cycle adjustment)
Because ovulation timing shifts with cycle length, the calculator nudges the date for cycles longer or shorter than 28 days. Gestational age then counts the weeks elapsed since that first day.
With a last period starting on 1 January and a 28-day cycle, the estimated due date is about 8 October — 280 days later. Conception is estimated around two weeks after the period began.
A guide, not a guarantee
A due date is a helpful anchor for planning, but birth rarely lands on it. Treating it as a window rather than a deadline takes some of the pressure off — and your care team’s dating, often confirmed by an early scan, is what counts.
Good to keep in mind
- It’s an estimate. A range of a couple of weeks either side is normal.
- Scans refine it. Early ultrasound dating is usually more accurate than dates alone.
- Care comes first. Follow your midwife or doctor for anything that matters.
This is general information, not medical advice.