Due Date Calculator

Your estimated due date (EDD) represents the date at which your pregnancy reaches 40 weeks of gestational age. This is the statistical midpoint of full-term delivery — most babies are born between 39 and 41 weeks.

The trimester milestones shown mark key developmental transitions: the first trimester ends at week 12 (major organ formation complete), the second trimester runs through week 27 (rapid growth and movement), and the third trimester begins at week 28 (lung maturation and weight gain).

If your provider gives you a different due date based on an ultrasound, their estimate may be more accurate — especially if the ultrasound was performed in the first trimester. ACOG recommends using the ultrasound-based EDD when there is a discrepancy of more than 5-7 days from the LMP-based date.

For twin pregnancies, the adjusted EDD of 37 weeks reflects the earlier expected delivery timing. Your care team will monitor growth more frequently and discuss delivery planning earlier than with a singleton pregnancy.

The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle with ovulation on day 14. For longer or shorter cycles, the calculator adjusts the ovulation offset accordingly.

The conception date method adds 266 days (38 weeks) to your known conception date — equivalent to 280 days from LMP minus the 14-day follicular phase.

For IVF transfers, we calculate the LMP equivalent using the known embryo age: transfer date minus (embryo age in days + 14 days). Then we add 280 days to that LMP equivalent.

With ultrasound dating, we back-calculate the LMP equivalent from the gestational age measured at the time of the scan, then add 280 days. Per ACOG guidelines, first-trimester ultrasound is the most accurate dating method.