Obstetrics
Pregnancy due date (EDD)
This estimates the expected date of delivery from the last menstrual period, from a dating ultrasound, or from a known conception date. Where an early scan disagrees materially with the dates, the scan is what obstetric practice uses.
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This calculator is provided for reference and education. It does not replace clinical assessment, examination, current guidelines, local protocol, or professional judgment. Verify every result before acting on it. Nirogix accepts no liability for clinical decisions made using this tool.
The formula
- Naegele: EDD = first day of the last menstrual period + 280 days, adjusted by (cycle length − 28)
- From a scan: EDD = scan date + (280 − gestational age in days at the scan)
- From conception: EDD = conception date + 266 days
Worked example
LMP on 01/01/2026 with a 28-day cycle → EDD 08/10/2026
When to use it
- Booking antenatal care and scheduling scans
- Interpreting fetal growth against gestation
And when not to
- Naegele assumes a regular 28-day cycle and reliable recall of the last period. Both fail often.
- A first-trimester scan dates a pregnancy more accurately than the last menstrual period, and where they disagree materially the scan is used.
- This is not a fertility or ovulation calculator.
References
- Methods for estimating the due date — ACOG Committee Opinion 700, 2017
Last reviewed 07/09/2026.
These calculators are free and always will be. We also build Nirogix, a hospital management system for Indian clinics and hospitals. The same calculations are planned inside the consultation record, pre-filled from the chart.