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 |
How to Use This Due Date Calculator
Enter the first day of your last menstrual period (LMP) or the date of conception. The calculator estimates your due date and shows your pregnancy timeline by trimester.
Formula & How It Works
Due Date = LMP + 280 days (Naegele's Rule). From conception: Due Date = Conception Date + 266 days. Only 5% of babies arrive on the exact due date.
Calculation Example
LMP of January 1, 2026: Due date = October 8, 2026. First trimester: weeks 1-12. Second: weeks 13-27. Third: weeks 28-40.
Expert Tips
Due dates are estimates β normal delivery ranges from 37-42 weeks. Ultrasound dating in the first trimester is more accurate than LMP calculation, especially with irregular cycles.
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.