How Due Dates Work
Due date = Last Menstrual Period + 280 days (40 weeks). Adjusted for cycle length differences from 28 days.
Pregnancy Timeline
| Trimester | Weeks | Milestones |
|---|---|---|
| First | 1-12 | Organ formation, heartbeat at 6 wks |
| Second | 13-26 | Movement felt, gender visible |
| Third | 27-40 | Rapid growth, lung maturity |
Frequently Asked Questions
How accurate is the due date?
Only 5% of babies are born on their exact due date. Most arrive within 1-2 weeks before or after.
Does cycle length affect due date?
Yes. Longer cycles mean later ovulation and a later due date. This calculator adjusts for cycle length.
When should I see a doctor?
Schedule your first prenatal visit at 8-10 weeks. An ultrasound at 8-12 weeks gives the most accurate due date.