Estimated Due Date Calculator (EDD)
Predict your baby’s arrival using Last Menstrual Period (LMP) or Conception Date.
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How Our Estimated Due Date Calculator Works
The Estimated Due Date Calculator provides an Estimated Due Date (EDD) by applying standard obstetrical rules. Consequently, the EDD is most commonly determined using the first day of the Last Menstrual Period (LMP). Since we calculate pregnancy from the start of the last cycle, the gestational period is typically counted as 40 weeks (or 280 days).
For those who have tracked ovulation or used assisted reproductive technology, using the Conception Date Calculator method provides a more precise starting point.
Naegele’s Rule (LMP Method)
Naegele’s rule is the standard method medical professionals use to estimate the due date. The formula is:
Alternatively, it can be calculated as LMP + 280 days. This assumes a standard 28-day cycle. If you are tracking other health metrics, you might also find our Pregnancy Weight Gain Calculator useful for monitoring your progress.
Trimester Definitions
Doctors track developmental milestones and necessary screenings by dividing pregnancy into three trimesters:
- First Trimester: Weeks 1 through 13
- Second Trimester: Weeks 14 through 27
- Third Trimester: Weeks 28 through 40
Frequently Asked Questions (FAQ)
Why is the Estimated Due Date Calculator so important?
Accurately estimating the due date is critical for both medical professionals and expecting parents. It allows doctors to monitor the baby’s growth against specific milestones and schedule important tests. In addition, it helps parents plan for the arrival, ensuring they prepare everything needed for the new baby within the appropriate time frame.
Is the estimated due date always correct?
No. The EDD is an estimate, and only about 4% of babies actually arrive on their exact due date. The majority arrive within a window of two weeks before or two weeks after the estimated date. Your doctor will use this calculation alongside ultrasound measurements for better accuracy. For more details on the LMP method, visit our guide on the Pregnancy Due Date Calculator (LMP Method).