Pregnancy Due Date Calculator
Estimate your due date from the first day of your last period or your conception date — and see how many weeks pregnant you are today and which trimester.
From the first day of your last period
Today's date is taken from your device clock. Estimates only — your midwife or doctor will use the dating scan as the official due date once it's available.
Formula
Two short formulas — pick the tab for what you have:
- From LMP:
due date = LMP + 280 days + (cycle length − 28). The cycle adjustment shifts ovulation, and so the due date, by the same number of days. - From conception:
due date = conception + 266 days.
Trimesters use the standard clinical boundaries: trimester 1 ends at 14 weeks 0 days, trimester 2 at 28 weeks 0 days, and trimester 3 runs from there to the due date.
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Frequently asked questions
How is the estimated due date (EDD) calculated?▾
The American College of Obstetricians and Gynecologists (ACOG) uses Naegele's rule by default: first day of last menstrual period (LMP) plus 280 days (40 weeks). That assumes a 28-day cycle with ovulation on day 14. ACOG's committee opinion on dating recommends that an early ultrasound (before 14 weeks) supersede the LMP date if the two disagree by more than 5–7 days, since first-trimester ultrasound dating is more accurate than menstrual dating.
What if my cycle isn't 28 days?▾
Adjust the cycle length input — each day longer than 28 shifts the estimated due date one day later, since ovulation (and conception) happens proportionally later. The calculator uses (cycle length − 28) as the adjustment. For very irregular cycles a first-trimester dating ultrasound is more reliable; that's the standard your OB-GYN will use to set the official due date if it's available.
Will my baby actually arrive on the due date?▾
Only about 4% of US babies are born on their exact estimated due date. Most arrive within roughly 37–42 weeks of LMP — what ACOG and the NIH define as 'term'. Specifically: early term (37 0/7 to 38 6/7), full term (39 0/7 to 40 6/7), late term (41 0/7 to 41 6/7), and post-term (42 0/7 and beyond). Induction is commonly discussed at 41 weeks and recommended by 42.
When does each trimester start?▾
Trimester 1 runs from LMP through week 13, trimester 2 from week 14 through week 27, and trimester 3 from week 28 to delivery. The boundaries are clinical conventions, not biological events — they roughly mark the end of organogenesis (T1), the more comfortable middle phase (T2), and the third-trimester growth phase (T3). Major prenatal milestones include the first prenatal visit at 8–10 weeks, the anatomy scan at 18–22 weeks, glucose screening at 24–28 weeks, and Group B Strep at 35–37 weeks.
When should I see my OB-GYN about a pregnancy?▾
ACOG recommends scheduling the first prenatal visit between 8 and 10 weeks. At that visit you'll typically have an exam, lab work (blood type, Rh status, infectious-disease screening), and often a dating ultrasound. Earlier contact is fine — and important if you have specific risk factors or pre-existing conditions — but the formal prenatal care schedule kicks off around weeks 8–10 with monthly visits through week 28, then more frequent visits later.