How Many Weeks Pregnant? Due Date Guide

Knowing your estimated due date helps you and your family prepare properly.

Naegele’s Rule

Estimated due date = first day of last menstrual period (LMP) + 280 days (40 weeks)

Example: LMP January 1, 2026

• Estimated due date: October 8, 2026

Gestational Age

Counted from LMP (not conception date), in weeks.

What to Know

• Only ~5% of babies arrive on the exact due date
• Normal range: 2 weeks before to 2 weeks after
• First-trimester ultrasound gives a more accurate estimate

Calculate Instantly

Use our Due Date Calculator — enter LMP, get due date + current pregnancy week. Free.