Due date, gestational age, and milestone schedule
An estimated due date is a clinical planning reference, not a prediction of the exact delivery day. Your maternity team may revise dating after an early ultrasound.
Pregnancy timeline
Evidence-based guide
Pregnancy dating provides a shared clinical timeline for prenatal testing, fetal growth, and delivery planning. Gestational age conventionally begins on the first day of the last menstrual period—about two weeks before conception in a typical cycle.
Adds 280 days and adjusts for cycle length. This is most useful when the LMP is certain and cycles are regular.
Subtracts the measured gestational age from the scan date. First-trimester ultrasound is often the most accurate clinical dating method.
Adds 266 days to conception; IVF dating additionally accounts for embryo age at transfer.
The result includes an estimated due date, current gestational age, trimester boundaries, and a 37–42 week term window. Only a small minority of births occur on the exact estimated date, so the surrounding window is more meaningful than one calendar day.
Dating can be revised by a clinician when LMP and ultrasound disagree. This tool cannot assess fetal growth, pregnancy viability, symptoms, or complications. Seek urgent care for heavy bleeding, severe pain, fainting, or other concerning symptoms.
Gestational age uses LMP because it is usually easier to identify than the exact date of ovulation or fertilization.
A known IVF timeline is precise; otherwise, an early first-trimester ultrasound is often the strongest clinical estimate.
Modern clinical terminology distinguishes early term, full term, late term, and postterm within the broader 37–42 week interval.
Yes. A maternity clinician may revise it based on ultrasound findings and the reliability of the menstrual history.
