How Pregnancy Due Date is Calculated

Pregnancy due date is typically calculated using Naegele's Rule: First day of last menstrual period + 280 days (40 weeks). This assumes a regular 28-day cycle.

Trimesters

• First Trimester: Weeks 1-12 — organ development, morning sickness
• Second Trimester: Weeks 13-27 — baby grows, movements felt
• Third Trimester: Weeks 28-40 — final growth, preparation for birth

Pregnancy Milestones

• Week 5: Heartbeat detectable
• Week 12: First trimester screening
• Week 20: Anatomy scan, gender can be determined
• Week 24: Viability milestone
• Week 37: Full-term begins
• Week 40: Due date

How Accurate is the Due Date?

Only about 5% of babies are born on their exact due date. Most births occur between weeks 38-42. An early ultrasound (before week 12) is the most accurate method to determine due date.

Factors That Affect Due Date

• Cycle length (longer cycles = later due date)
• Irregular periods
• Multiple pregnancy (twins usually delivered earlier)
• Mother's age and health
• Previous pregnancy history

Important Note

This calculator gives an estimate. Always follow your OB-GYN's advice for accurate dating, prenatal care, and monitoring. Regular checkups are essential for a healthy pregnancy.

Why Use Our Calculator?

Get a quick estimate of your due date and current pregnancy week. Track your journey with confidence.