Pregnancy Due Date Calculator
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How to use
- 1 Pick the method you have most reliable data for: LMP (last menstrual period), conception date, or ultrasound CRL.
- 2 For LMP: enter the first day of your last menstrual period and your average cycle length (default 28 days).
- 3 For conception: enter the known date — used for IVF transfers or single-encounter conception.
- 4 For ultrasound: enter the scan date and CRL measurement in mm (works best 7–13 weeks).
- 5 Click Calculate to see your due date, current gestational age, weeks remaining, trimester, and prenatal milestone dates.
About Pregnancy Due Date Calculator
FAQ
Q How accurate is a due date calculated from my last period?
LMP-based dating using Naegele's rule is reasonably accurate when cycles are regular at 28 days and you remember the LMP confidently. Studies cited by ACOG show that about 40% of women have their due date adjusted by more than 5 days after a first-trimester ultrasound, so the scan is the gold standard.
Q When does ACOG recommend changing the due date?
Per ACOG Committee Opinion 700, the ultrasound EDD should replace the LMP EDD if they differ by more than 5 days when ultrasound is performed at 8w 6d or earlier; more than 7 days for 9w 0d–15w 6d; more than 10 days for 16w 0d–21w 6d; and more than 14 days for 22w 0d–27w 6d.
Q How is the due date calculated for IVF pregnancies?
For IVF, the conception date is precisely known. EDD = transfer date + 263 days for a day-3 embryo, or transfer date + 261 days for a day-5 blastocyst. Equivalently, EDD = embryo creation date + 266 days. Always confirm with your fertility clinic which dating their lab uses.
Q What if my menstrual cycle is not 28 days?
Adjust ovulation timing. Ovulation occurs roughly 14 days before the next period regardless of cycle length, so a 32-day cycle ovulates around day 18 (not day 14). For a 32-day cycle, the EDD by LMP is approximately LMP + 284 days. Cycle-adjusted calculations are more accurate; use the calculator's cycle length input.
Q When does the second trimester start?
The second trimester begins at 14 weeks 0 days of gestational age (counting from LMP) and ends at 27 weeks 6 days. The third trimester begins at 28 weeks 0 days. ACOG and the CDC both use these standardized week boundaries.
Q What percentage of babies are born on the actual due date?
About 5%. Around 70% of healthy singleton pregnancies deliver within ±10 days of the EDD. Per ACOG, 37–42 weeks is the normal full-term window. First-time mothers tend to deliver slightly later (median ~40w 5d) than mothers with prior births.
Q Is it safe to deliver at 37 weeks?
ACOG classifies 37w 0d–38w 6d as "early term" — generally safe but associated with slightly higher risk of feeding, breathing, and temperature regulation issues than 39w 0d–40w 6d ("full term"). Elective deliveries before 39 weeks are not recommended without medical indication.
Q How do I count pregnancy weeks correctly?
Pregnancy weeks count from the first day of the LMP, not from conception. So at "8 weeks pregnant" you're actually about 6 weeks past conception. This dating convention is universal in obstetrics so anatomy scans, blood tests, and milestones are all measured the same way.
Official resources
ACOG Committee Opinion 700 — Methods for Estimating Due Date
Authoritative US obstetrics standard for pregnancy dating from the American College of Obstetricians and Gynecologists.
CDC — Pregnancy Health and Care
Centers for Disease Control consumer guidance on pregnancy care, screening, and risk factors.
ACOG — Patient FAQ on Healthy Pregnancy
ACOG patient education resources, including timing of prenatal visits and screening tests.
NIH NICHD — Pregnancy Information
NIH Eunice Kennedy Shriver National Institute of Child Health and Human Development pregnancy resources.