EDD Calculator

Estimate a due date and see gestational age today from the strongest available dating source.

What should we use?

First day of the last normal menstrual period

Calculation date—

Estimated due date

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Gestation today

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Pregnancy stage—

Review and copy assessment

Complete the required assessment to enable copying.

Guidance and sources

Kenyan practice and facility protocol remain controlling. ACOG dating guidance is supplementary.

Dating method guide

Use one established date and keep its limits visible.

Choose the best-supported dating basis available. Once an EDD is established, a later ultrasound is usually used to assess growth rather than casually replace the original date.

01 / LMP

Last normal menstrual period

Add 280 days to the first day of the last normal menstrual period. This is the Naegele-style baseline used here and assumes an average 28-day cycle.

Best when: The first day is certain and cycles are regular.
Accuracy: Limited by recall and variation in ovulation timing.

02 / FIRST-TRIMESTER SCAN

Document the measurement basis

Enter the scan date and its recorded gestational age. A reported week alone does not establish first-trimester dating precision.

1+0–5+6: This tool withholds a numerical range as a precaution; check the scan report and measurement. This is not a viability cutoff.
6+0–13+6: With documented crown–rump length dating, typical precision is ±5–7 days.

03 / ULTRASOUND DATING

Use the gestation recorded at the scan

For scans from 14+0 weeks onward, the typical precision comes from the recorded gestation at that scan, whether it was the first or latest scan. Later fetal size is influenced by growth, so an established EDD should not be casually replaced.

14+0–21+6 ±7–10 days22+0–27+6 ±10–14 days28+0 and later ±21–30 days

These ranges mean: Typical dating precision, not a delivery window.
At 40+6 or later: The late-scan caution remains; check the report and established dating basis.

References