Due Date Calculator
Calculate your pregnancy due date from your last period or conception date.
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Estimated Due Date
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End of 1st Trimester
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End of 2nd Trimester
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Current Week
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Likely Conception
About the Due Date Calculator
This calculator uses Naegele's rule, the standard method used by obstetricians worldwide. It adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a standard 28-day cycle. Our calculator adjusts for cycle lengths between 21 and 45 days.
Pregnancy milestones
- Week 12: End of first trimester — risk of miscarriage drops significantly
- Week 20: Anatomy scan — detailed ultrasound examination
- Week 28: Third trimester begins
- Week 37: Baby is considered full term
- Week 40: Estimated due date
Always confirm your due date with a qualified healthcare provider. Ultrasound measurements in early pregnancy provide the most accurate dating.
Frequently Asked Questions
How is a due date calculated?
The most common method (Naegele's rule) adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle. Your healthcare provider may adjust this based on ultrasound measurements.
How accurate is the due date?
Only about 5% of babies are born on their exact due date. Most births occur within two weeks either side. The due date is a best estimate based on average pregnancy length.
What are the pregnancy trimesters?
The first trimester runs from week 1 to week 13. The second trimester is weeks 14–27. The third trimester is weeks 28–40 (birth).
Can I calculate due date from conception?
Yes. If you know your conception date, add 266 days (38 weeks) to get your estimated due date. However, conception date is often hard to pinpoint exactly, making LMP-based calculation more practical.