Enter your last menstrual period date and instantly calculate your estimated due date, current pregnancy week, trimester, and days until your baby arrives.
Based on Naegele's Rule (LMP + 280 days). Confirm with your first ultrasound.
A pregnancy due date calculator estimates your baby's expected date of arrival — called the Estimated Due Date (EDD) — based on the first day of your last menstrual period (LMP). This is the same method used by obstetricians worldwide. The formula adds 280 days (40 weeks) to your LMP date, following Naegele's Rule.
Naegele's Rule: EDD = LMP + 280 days. This accounts for the 2-week gap between LMP and ovulation, plus 38 weeks of fetal development. Your OB-GYN uses this at your first prenatal visit and refines it with your 8–12 week ultrasound.
| Trimester | Weeks | Key Developments |
|---|---|---|
| 1st Trimester | Weeks 1–13 | All major organs form. Morning sickness peaks weeks 8–10. |
| 2nd Trimester | Weeks 14–27 | Energy returns. Baby movements begin (weeks 18–22). |
| 3rd Trimester | Weeks 28–40 | Rapid baby growth. Braxton Hicks, back pain common. |
| Week | Milestone |
|---|---|
| Week 6–8 | First prenatal visit, heartbeat detected on ultrasound |
| Week 12 | End of highest-risk period, first-trimester screening |
| Week 20 | Anatomy ultrasound — gender can be revealed |
| Week 24 | Viability milestone — baby can survive with intensive support |
| Week 28 | Third trimester begins, biweekly OB visits start |
| Week 37 | Full term — baby is ready for birth ✅ |
| Week 40 | Due date arrives! 🎉 |
Medical Disclaimer: This tool is for educational purposes only. Due date estimates may vary. Always consult a qualified OB-GYN for personalized pregnancy care.
Your pregnancy due date — also called your estimated date of delivery (EDD) — is calculated using Naegele's Rule, the standard method used by OB-GYNs worldwide. The formula adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This accounts for the fact that conception typically occurs about 2 weeks after your period begins, and a full-term pregnancy lasts 38 weeks from conception.
It's important to know that only about 5% of babies arrive on their exact due date. Most healthy births occur within a 2-week window on either side — between 38 and 42 weeks of pregnancy. Your due date is your best estimate, not an exact deadline.
Pregnancy is divided into three trimesters. The first trimester covers weeks 1–13 and is when all major organs and structures form. The second trimester spans weeks 14–27 — often called the "honeymoon phase" as energy returns and nausea eases. The third trimester runs from week 28 until birth, during which your baby gains most of its weight and prepares for life outside the womb.