Gestational age and due date calculator
Find the gestational age on a chosen date and the estimated due date from the last menstrual period, a known due date or an ultrasound.
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- Gestational age (weeks + days)
- Estimated due date
- First day of the last menstrual period (calculated)
How it is calculated
Pregnancy is counted as 280 days (40 weeks) from the first day of the last menstrual period, the usual rule used for due dates.
Only the calendar is calculated; dates are not sent anywhere. Clinical dating belongs to your doctor or midwife.
Due date = first day of the last period + 280 daysGestational age = date − first day of the last period
Worked example: Last period 1 January 2024: due date 7 October 2024; on 11 March 2024 the age is 10 weeks + 0 days.
Sources
These calculators support research; they do not replace the advice of a statistician or a clinician.
Questions
Which date should I trust most?
A reliable last menstrual period is used when it agrees with an early ultrasound; otherwise dating by early ultrasound is preferred. This tool only does the arithmetic and gives no clinical advice.