Pregnancy Due Date Calculator
Estimate your due date from last period, conception, IVF transfer or ultrasound dating. See how far along you are, trimester progress and key dates.
Calculate
Estimated due date
The formula
LMP dating adds 280 days (40 weeks), adjusted for cycle length. Conception dating adds 266 days. IVF uses transfer day (day-3 ≈ +263, day-5 ≈ +261). Ultrasound projects the due date from gestational age at the scan.
Worked example
- LMP = 24 September 2026 · cycle 28 days
- Due date = LMP + 280 days → 1 July 2027
- On 9 October 2026 → 2 weeks 1 day pregnant
Result: Estimated due date: Thursday, 1 July 2027
How due dates are estimated
A due date is a midpoint estimate, not a promise. Most births occur in a window around that day.
Last period (Naegele)
We add 280 days (40 weeks) to the first day of your last menstrual period, then adjust by (cycle length − 28) so longer cycles move the due date later.
Count the first day of bleeding, not spotting. Irregular cycles or recent hormonal contraception reduce reliability — your clinician may prefer ultrasound dating.
Conception dating
When the conception date is known, dating often adds about 266 days (38 weeks) from conception — equivalent to a typical LMP about two weeks earlier.
IVF transfer
Day-3 embryo transfer commonly adds about 263 days; day-5 (blastocyst) about 261 days. Always prefer your clinic’s official dating if it differs.
Ultrasound
Enter the scan date and gestational age reported that day. We project a due date as scan date + (280 − gestational age in days). First-trimester crown–rump length is often preferred when LMP is uncertain.
Term windows
Full term here means 39 weeks 0 days through 40 weeks 6 days. Early term, late term and post-term categories still matter clinically — this tool highlights the common full-term window around your due date.
Interesting facts
Named after Franz Naegele
German obstetrician Franz Karl Naegele popularized the LMP-plus-~280-days rule that still anchors many prenatal charts.
Only about 5% deliver on the day
Most births occur within about two weeks of the estimated due date. Midwife or obstetric follow-up refines timing with exams and ultrasound.
LMP vs conception dating
LMP dating assumes a typical cycle with ovulation around day 14. Known conception or embryo transfer dates change which day count applies.
Ultrasound adjustments
Early ultrasound dating is preferred when cycle history is uncertain; later scans primarily track growth against the agreed due date.
Full-term is a range
Clinical categories such as early term and full term emphasize a window of readiness rather than one calendar day.
Frequently asked questions
Add 280 days (40 weeks) to the first day of your last menstrual period, then adjust if your average cycle is not 28 days. Your clinician may revise after ultrasound.
Switch to Conception mode — we add about 266 days from conception. IVF patients should use IVF transfer mode or their clinic’s date.
Choose day-3 or day-5 transfer. We add about 263 or 261 days respectively. Clinic protocols can differ — follow the date on your paperwork.
Yes. Enter the scan date and the gestational age shown that day. We project the 40-week due date from that measurement.
Obstetric weeks traditionally count from LMP, about two weeks before ovulation/conception in a 28-day cycle — so 40 weeks LMP ≈ 38 weeks from conception.
It is an estimate for planning. Dating scans and clinical judgment often adjust the due date, especially with irregular cycles or uncertain LMP.
References
- Methods for estimating the due date Clinical guidance on LMP vs ultrasound dating.
- Definition of term pregnancy Early-term, full-term, and related definitions.
- Antenatal care recommendations Global context for pregnancy care and timing discussions.