Decision tools built for clarity
Pregnancy Due Date Calculator
Estimate an educational due date from a last menstrual period or conception date.
Choose last menstrual period or conception as the dating basis, then enter that date.
This pregnancy date is an educational estimate, not clinical dating or medical advice; ultrasound and a qualified clinician may revise it.
Methodology
Formula or transformation
Derives educational pregnancy dates from the submitted basis date and fixed gestational day offsets.
Variables
- Submitted reference date
- Estimated gestational start
- Conception-date offset in days
- Due-date offset in days
- Gestational milestone weeks
Units
- Calendar date
- Day
- Week
Rounding policy
Calendar results use whole-day offsets; no fractional date is displayed.
The estimate uses 280 days from the last menstrual period or 266 days from conception and derives a bounded milestone schedule.
Estimate an educational due date from a last menstrual period or conception date.
Reviewed sources
- ACOG — When pregnancy goes past your due date Reviewed on 2026-09-05
- ACOG — How your fetus grows during pregnancy Reviewed on 2026-09-05
- NIH MedlinePlus — Fetal development Reviewed on 2026-09-05
Formula review history
-
Initial formula and source review.
Reviewed 2026-09-04 for formula version educational-due-date-v1
-
Source review: replaced a newborn-anthropometry study with the NIH MedlinePlus fetal development entry and re-confirmed both ACOG pages for the 280-day and 14-day conventions.
Reviewed 2026-09-05 for formula version educational-due-date-v1
Assumptions
- The entered last-menstrual-period or conception date matches the selected basis.
- The 280-day LMP or 266-day conception convention is appropriate for this estimate.
Limitations
- Cycle length, uncertain dates, assisted reproduction, and clinical findings can change pregnancy dating.
- Only a qualified clinician can establish or revise clinical dating, often using ultrasound and medical history.
Worked example
A last menstrual period beginning 1 January 2026 gives an estimated due date of 8 October 2026 using the 280-day convention.
Frequently asked questions
Is the estimated due date exact?
No. It is a conventional estimate and births commonly occur before or after it.
Can this replace an ultrasound date?
No. Follow the dating and care plan provided by a qualified maternity clinician.