How Due Date Is Calculated
The estimated due date (EDD) is most commonly calculated using Naegele's Rule, developed in the 19th century by German obstetrician Franz Karl Naegele. The rule adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).
Naegele's Rule Formula
Due Date = LMP date + 280 days
OR
Due Date = LMP date + 9 months + 7 days
OR
Due Date = LMP date + 9 months + 7 days
Pregnancy Timeline
| Trimester | Weeks | Key Milestones |
|---|---|---|
| First Trimester | Weeks 1–12 | Organ development, morning sickness, first heartbeat ~week 6 |
| Second Trimester | Weeks 13–26 | Baby movements felt, anatomy scan at ~20 weeks |
| Third Trimester | Weeks 27–40 | Rapid growth, lung maturation, baby positions for birth |
When to seek medical care: Visit your doctor as soon as you confirm your pregnancy. First prenatal appointment is typically at 8–10 weeks. Regular checkups every 4 weeks until week 28, then every 2 weeks.