Pregnancy Due Date Estimator
Enter the first day of your last menstrual period (LMP) and cycle length to calculate the estimated date of delivery (EDD). Optionally, add ultrasound data to refine the estimate.
Adjusts Naegele’s rule for shorter or longer cycles.
Optional ultrasound dating
Use the gestational age provided on the ultrasound report (e.g., 8 weeks 2 days).
How to Use This Calculator
Record your LMP
The first day of bleeding counts as day 1 of your menstrual cycle and forms the basis of Naegele’s rule.
Adjust for cycle length
Longer or shorter cycles shift ovulation timing. Use your average length if it differs from 28 days.
Add ultrasound data for refinement
Input the earliest ultrasound to corroborate or update the due date, especially if periods are irregular.
Formula
Naegele’s rule: EDD = LMP + 280 days − (28 − cycle length)
Ultrasound dating: EDD = Ultrasound date − (GA weeks × 7 + GA days) + 280
Trimester milestones: End of first trimester ≈ 13w6d, second trimester ≈ 27w6d
Full Description
The estimated date of delivery (EDD) marks 40 weeks of gestation from the last menstrual period. Because ovulation rarely occurs on cycle day 14 for everyone, ultrasound dating—particularly crown-rump length in first trimester—is the preferred method to confirm or adjust the due date. Accurate dating guides prenatal screening windows, growth monitoring, and timing of delivery if complications arise.
Frequently Asked Questions
How accurate is the due date?
Even with accurate dating, only ~5% of births occur on the exact due date. It is better viewed as a 40-week milestone.
What if I have irregular cycles?
Use the ultrasound-based EDD as the primary reference. Irregular cycles can make LMP-based dating unreliable.
Do IVF pregnancies use the same calculator?
IVF due dates are calculated differently based on embryo transfer date and embryo age; see the EDD calculator for IVF-specific calculations.
Can the due date change later in pregnancy?
Generally no. Once established, the due date remains the same unless significant discrepancies arise early on.