How is a Due Date Calculated?
Pregnancy due dates are typically calculated using Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method assumes a 28-day cycle with ovulation occurring on day 14.
Why Use the Last Menstrual Period?
Most healthcare providers use the LMP method because:
- Women typically remember the start of their period more accurately than ovulation
- It provides a standardized method for calculating due dates
- Only about 5% of babies are born exactly on their due date
- It establishes a consistent timeline for prenatal care milestones
Pregnancy Timeline and Trimesters
- First Trimester (Weeks 1-13): Early development, morning sickness, initial prenatal visits
- Second Trimester (Weeks 14-27): Baby's movements felt, anatomy scan, more energy
- Third Trimester (Weeks 28-40+): Rapid growth, preparation for birth, frequent checkups
Factors That Can Affect Your Due Date
- Cycle Length: Women with longer cycles may ovulate later
- Irregular Periods: Can make LMP dating less accurate
- Early Ultrasound: First-trimester ultrasounds provide the most accurate dating
- IVF Pregnancy: Exact conception date is known
When to See a Healthcare Provider
While this calculator provides an estimate, it's important to:
- Schedule your first prenatal appointment after a positive pregnancy test
- Confirm your due date with a healthcare professional
- Follow recommended prenatal care schedules
- Discuss any concerns about your pregnancy timeline with your provider
Understanding Your Results
- Estimated Due Date (EDD): The calculated date when your baby is most likely to arrive
- Gestational Age: How far along you are in your pregnancy
- Conception Date: The approximate date when fertilization occurred
- Trimesters: The three main stages of pregnancy
- Note: Only about 5% of babies are born exactly on their due date