Pregnancy Due Date Calculator
Calculate your pregnancy due date (EDD). Free online pregnancy calculator — enter last menstrual period (LMP) date to get estimated delivery date and current week.
How to Use
- Enter the first day of your Last Menstrual Period (LMP).
- Enter your average menstrual cycle length (default 28 days).
- Click Calculate to get your Estimated Due Date (EDD) and current pregnancy week.
Formula
Naegele's Rule: EDD = LMP + 280 days (40 weeks)
Adjustment for cycle: Add (Cycle Length − 28) days to the EDD
40 weeks from LMP = average pregnancy duration
Example Calculation
Example: LMP = January 1, 2025, 28-day cycle
| Parameter | Value |
|---|---|
| Last Menstrual Period | January 1, 2025 |
| Cycle Length | 28 days |
| Estimated Due Date | October 8, 2025 |
| 1st Trimester | Weeks 1–13 |
| 2nd Trimester | Weeks 14–26 |
| 3rd Trimester | Weeks 27–40 |
Frequently Asked Questions
The EDD is an estimate. Only 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the EDD. An ultrasound in the first trimester gives the most accurate dating.
If you have irregular cycles, the LMP-based calculation may be less accurate. Your doctor will use an early ultrasound (preferably at 7–12 weeks) to give a more accurate EDD.
1st Trimester: Weeks 1–13 (organ formation). 2nd Trimester: Weeks 14–26 (rapid growth, gender visible). 3rd Trimester: Weeks 27–40 (lung development, weight gain).
Full-term is 39–40 weeks. Early term: 37–38 weeks. Late term: 41 weeks. Post-term: 42+ weeks. Babies born before 37 weeks are considered premature.
Schedule your first prenatal visit at 6–8 weeks. Your doctor will confirm the pregnancy, check for multiples, and establish an accurate due date via ultrasound.
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