Pregnancy Due Date Calculator
Understanding Pregnancy Due Dates
How Due Dates Are Calculated
The standard pregnancy calculation uses Naegele's Rule:
- Start with the first day of your last menstrual period (LMP)
- Add 7 days
- Subtract 3 months
- Add 1 year
This estimates a 40-week pregnancy, though only about 5% of women deliver on their exact due date.
Key Pregnancy Milestones
| Trimester | Weeks | Key Developments |
|---|---|---|
| First | 1-12 | Organ formation, morning sickness |
| Second | 13-26 | Gender visible, quickening |
| Third | 27-40 | Rapid growth, position for birth |
Factors That Affect Due Date Accuracy
- Irregular cycles: Our calculator adjusts for cycle length
- Early ultrasound: Most accurate between 8-12 weeks
- IVF pregnancies: Use embryo transfer date instead
Did You Know? Only about 5% of babies are born on their exact due date. Most arrive between 37-42 weeks.