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Estimate your due date using three methods: last menstrual period (Naegele's Rule), conception date, or ultrasound dating. Includes current gestational age, trimester tracking, pregnancy progress bar, and key milestone timeline.
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Try tool →Naegele's Rule: Due date is 280 days (40 weeks) from the first day of your LMP.
A due date is an estimate of when your baby will be born, calculated as 40 weeks (280 days) from the first day of your last menstrual period. Only about 5% of births occur exactly on the due date. A full-term pregnancy ranges from 37 to 42 weeks.
Factors that affect due date accuracy:
Weeks 1-13
Rapid development of all major organs and systems. Common symptoms include fatigue, nausea, and breast tenderness.
Weeks 14-27
Baby grows significantly. Many women feel more energetic. Baby movements become noticeable.
Weeks 28-40+
Baby gains weight and matures. The body prepares for labor. Braxton Hicks contractions may occur.
Due dates calculated from LMP have a margin of error of about 1-2 weeks. First-trimester ultrasound dating is the most accurate method (±5-7 days). Remember that a "normal" pregnancy can range from 37-42 weeks, so your baby may arrive earlier or later than the estimated date.
Ultrasound measures the baby's size (crown-rump length in first trimester, head circumference, femur length, and abdominal circumference in later trimesters) and compares it to standard growth charts to estimate gestational age. The due date is then calculated as 40 weeks from the estimated start of pregnancy.
Naegele's Rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer, you may ovulate later and your due date should be adjusted accordingly. For a 35-day cycle, add 7 days to the calculated due date. For a 21-day cycle, subtract 7 days. Your healthcare provider will typically use ultrasound dating for the most accurate estimate.
Going past 40 weeks is common — about 60% of first-time mothers deliver after 40 weeks. Post-term pregnancy is defined as 42+ weeks. Healthcare providers typically recommend additional monitoring starting at 41 weeks and may discuss induction between 41-42 weeks.
Yes. Most twin pregnancies deliver between 34-37 weeks (vs 37-42 for singletons). The calculator provides a 40-week estimate based on standard dating, but your healthcare provider will adjust the expected delivery window based on the type of twins and overall pregnancy health.