Due Date Calculator — When Is Your Baby Due?
Calculate your estimated due date based on last menstrual period or conception date. See your pregnancy timeline with key milestones for each trimester.
Pregnancy due date calculation uses Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. While this gives an estimated due date only about 5% of babies arrive exactly on their due date. Most full-term babies arrive between 37-42 weeks. Our calculator shows your complete pregnancy timeline including when each trimester begins key milestone dates and the range of dates your baby is most likely to arrive.
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Key Information
| Parameter | Details |
|---|---|
| Average Pregnancy Duration | 280 days (40 weeks) from LMP |
| Full Term Range | 37 - 42 weeks |
| First Trimester | Weeks 1-12 |
| Second Trimester | Weeks 13-26 |
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Use Calculator NowFrequently Asked Questions
How accurate is the due date calculator?
Due date calculators based on LMP are accurate within 1-2 weeks for women with regular 28-day cycles. An early ultrasound (8-12 weeks) is considered the most accurate method for dating pregnancy accurate to within 3-5 days. If your cycle is irregular longer or shorter than 28 days the LMP-based date may be less accurate and your doctor may adjust based on ultrasound measurements.
What are the pregnancy trimester milestones?
First trimester (1-12 weeks): heartbeat detected at 6 weeks major organs forming morning sickness peaks. Second trimester (13-26 weeks): gender visible at 16-20 weeks baby movements felt at 18-22 weeks anatomy scan at 20 weeks. Third trimester (27-40 weeks): baby viable outside womb from 24 weeks lungs mature at 34-36 weeks full term at 37 weeks.
How is due date calculated with irregular periods?
With irregular periods LMP-based calculation may be inaccurate. Your doctor will rely on early ultrasound dating which measures crown-rump length to estimate gestational age. If you know your conception date add 266 days for estimated due date. Ultrasound dating is most accurate before 12 weeks and becomes the official due date if it differs from LMP calculation by more than 7 days.
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Last updated: 24 March 2026