Pregnancy Due Date

The most common method is Naegele's Rule: Add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. Only about 5% of babies arrive exactly on their due date — most come between 37 and 42 weeks.

Due dates are estimates, not guarantees. Only 5% of babies arrive exactly on their due date. 80% arrive between 38 and 42 weeks. First-time moms often go past their due date. Ultrasounds in the first trimester are most accurate for dating pregnancy.

If your cycles are irregular, the LMP method may not be accurate. Your doctor will use an early ultrasound (around 8-12 weeks) to determine gestational age and due date. The first trimester ultrasound is the most reliable method.

LMP (Last Menstrual Period) is the first day of your last period. Conception usually happens about 14 days after LMP (around ovulation). Due date is calculated from LMP, not conception. If you know your conception date, add 266 days.

First trimester: Week 1-12 (early development). Second trimester: Week 13-27 (growth and movement). Third trimester: Week 28-40 (final development and preparation for birth). Each trimester has different milestones and symptoms.

Schedule your first prenatal visit around 8 weeks after your LMP. Earlier if you have medical conditions, previous complications, or are over 35. The first visit typically includes confirmation ultrasound, blood tests, and health history review.