Quick answer: your estimated due date is typically 280 days (40 weeks) from the first day of your last menstrual period. Use our free Due Date Calculator for an instant estimate.
How the Estimate Works
Pregnancy is dated from the first day of your last period, not from conception, since ovulation date is often unknown. This means the "40 weeks" of pregnancy actually includes about 2 weeks before conception typically occurred.
Trimesters
Pregnancy is divided into three trimesters: first (weeks 1-13), second (weeks 14-27), and third (weeks 28-40+). Each carries distinct developmental milestones.
Frequently Asked Questions
How accurate is a due-date calculation?
Only about 5% of babies arrive exactly on their estimated due date — it's a helpful estimate, not a guarantee, with most births occurring within 2 weeks either side.
Can I calculate from conception date instead?
Yes, if you know your conception date, add 266 days for an alternative estimate.
Should I confirm this with a doctor?
Yes — an ultrasound-based estimate from a healthcare provider is more precise than a calendar-based calculation.
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