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**Medical Disclaimer:** The information provided by this calculator is for educational and informational purposes only and should not be considered as medical advice. Always consult with a qualified healthcare provider before making any decisions about your health or treatment. This tool is not intended to diagnose, treat, cure, or prevent any disease.
Due dates are estimates. Only about 5% of babies are born on their exact due date. Regular prenatal care is essential.
Learn how due dates are estimated, why they can change, and which milestones matter during pregnancy.
Common questions about due dates, gestational age, and prenatal timing
The most common method, called Naegele’s rule, estimates your due date as 280 days or 40 weeks from the first day of your last menstrual period. This assumes a 28-day cycle with ovulation around day 14, so results can shift if your cycles are shorter, longer, or irregular.
A due date is an estimate, not a guarantee. Only about 5% of babies are born on their exact due date. First-trimester ultrasound dating is usually more accurate than last-period dating, especially when cycle dates are uncertain.
Yes. If an early ultrasound measurement differs enough from your period-based estimate, your healthcare provider may update the official due date. Ultrasounds performed in the first trimester are generally the most accurate for dating pregnancy.
If you do not know your last menstrual period, a healthcare provider can estimate gestational age using ultrasound measurements and clinical history. Avoid relying only on symptoms or a positive pregnancy test date for dating.
Gestational age is the age of the pregnancy measured from the first day of the last menstrual period, not from conception. This is why pregnancy is counted as about 40 weeks even though conception usually happens around 2 weeks after the last period begins.
Many people schedule their first prenatal visit around 8 weeks of pregnancy, though timing can vary. Contact your healthcare provider sooner if you have pain, bleeding, chronic medical conditions, prior pregnancy complications, or are taking medications that may affect pregnancy.
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