This calculator estimates a due date, gestational age, and key pregnancy milestones for anyone tracking a current pregnancy.
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Enter the first day of the last menstrual period and, if available, the usual cycle length. Use an ultrasound date instead when a clinician has revised the pregnancy dating.
For a 28-day cycle, estimated due date = first day of the last menstrual period + 280 days. Gestational age = current date - first day of the last menstrual period, with the due date adjusted by cycle length - 28 days.
If the last menstrual period began January 1, 2026, and the usual cycle is 28 days, the estimated due date is October 8, 2026. On March 12, the estimated gestational age is 10 weeks.
The exact conception date is often unknown, so clinical dating starts from the last menstrual period. This adds roughly two weeks before conception to the stated gestational age.
Yes. An early ultrasound may provide better dating when cycles are irregular or its estimate differs enough from menstrual dating, so follow the date given by the clinician.
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