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Due date and gestational age

Expected date of delivery from the last menstrual period, with today’s gestational age in weeks and days and the trimester it falls in.

An illustration of a clinic toolkit: calculators, checklists, guides and reports

First day of last menstrual period

Fill the fields above and the answer appears here, with the working spelled out — the same working the in-product version saves to the chart.

Nothing you type here is sent anywhere. The calculation runs in your browser and the page keeps no record of it.

How it is worked out

Naegele’s rule: LMP + 280 days. Gestational age is counted from the same LMP, so the two answers can never disagree with each other.

What it does not do

It assumes a 28-day cycle and a certain LMP date. Where the cycle is irregular or the date is unsure, a first-trimester ultrasound dates the pregnancy better and should win.

It is a calculator, not a clinician. Nothing here is medical advice, and the person prescribing owns the decision.

Save this to a patient’s chart

That is the one thing this page cannot do. Inside MedAppz the same calculator writes the value and its working onto the record, so a year later anybody reading the chart can see which numbers produced it. 15 more calculators come with it.

Set up a practice See it in the demo clinic

The other calculators

BMI and body surface area eGFR (CKD-EPI 2021)Paediatric dose Corrected sodium Corrected calcium