Pregnancy Details
weeks
days
Used to adjust due date for non-28 day cycles (LMP method only)
How Is a Due Date Calculated?
The most common method is Naegele's Rule: Add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the due date is adjusted accordingly.
Trimester Breakdown
- First Trimester: Weeks 1–13 (conception, major organ development, risk of miscarriage)
- Second Trimester: Weeks 14–27 (fetal movement, anatomy scan, gender reveal possible)
- Third Trimester: Weeks 28–40 (rapid growth, lung development, delivery preparation)
Why Due Dates Are Estimates
Only about 5% of babies are born exactly on their due date. Most births occur within 2 weeks before or after the estimated date. A full-term pregnancy is considered 39–40 weeks; births between 37–42 weeks are considered "term."
Disclaimer
This calculator provides estimates for informational purposes only. Always consult your OB-GYN or midwife for accurate dating, which is typically confirmed by an early ultrasound.