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—

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 / EARLY SCAN

First accurate ultrasound

Enter the scan date and its recorded gestational age. A first-trimester scan using crown–rump length is the most accurate ultrasound method for establishing or confirming gestational age.

Best when: LMP is uncertain, cycles are irregular or an early scan is available.
Accuracy: About ±5–7 days through 13+6 weeks.

03 / LATER SCAN

Latest ultrasound

Enter the scan date and gestational age only when a reliable earlier dating basis is not available. Later fetal size is influenced by growth, so dating becomes less precise.

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

Best when: No reliable LMP or earlier dating scan is available.
Accuracy: Less precise after the first trimester; interpret with clinical context.

References