Pregnancy Due Date and Gestational Age Calculator
Estimate a due date and gestational age from the last menstrual period.
This is an estimate. Use the dates confirmed by your prenatal care professional.
Common values
About this tool
Estimate the due date and gestational age from the first day of the last menstrual period, cycle length, and a reference date. The calculation uses 280 days for a 28-day cycle and displays the cycle adjustment.
The conventional estimate is 280 days, or 40 weeks, from the first day of the last menstrual period for a 28-day cycle.
The cycle-length adjustment assumes ovulation shifts with the cycle. Irregular cycles or uncertain dates can make the estimate inaccurate.
Clinical dating may be confirmed or revised using early ultrasound. This calculator does not replace prenatal care or medical advice.
FAQ
- How is the estimated due date calculated?
- For a 28-day cycle, 280 days are added to the first day of the last period. The difference from 28 days is added or subtracted for another entered cycle length.
- When does gestational age start?
- This calculation counts the first day of the last period as 0 weeks, 0 days. It does not start at conception, so it usually begins about two weeks before the estimated ovulation date.
- Can this be used with irregular cycles?
- Values can be entered, but the adjustment assumes cycle length shifts ovulation by the same amount. Uncertain dates or irregular cycles can produce a larger error.
- What if a clinician gives a different due date?
- Use the date confirmed or revised by the prenatal care professional. Clinical dating based on early ultrasound and other information can differ from calendar estimation.
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