Obstetrics · Dating

Gestational Age Calculator

Calculate how many weeks pregnant you are today, your estimated due date, and key milestone dates through the pregnancy.

Work it out from

Choose whichever date you know.

Last menstrual period Estimated due date

First day of last menstrual period

Usual cycle length (days, if known)

Calculate as of (defaults to today)

Please enter a valid date.

Estimated due date

Trimester

Milestone	Gestation	Date

Estimate only. Gestational age is most accurate when confirmed by an early dating ultrasound (ideally 8–14 weeks). If your dating scan gave a different estimated due date to the one calculated here, the scan-based date should generally be used — discuss this with Dr McCaffrey.

Method: Naegele's rule (280 days / 40 weeks from the last menstrual period), adjusted for cycle length. Reference: Mercy Perinatal Toolkit.