EDD Calculator - Estimated Date of Delivery
Calculate your estimated due date using last menstrual period or ultrasound data
Calculate Your Due Date
Method 1: Last Menstrual Period (LMP)
Date when your last period started
Typical range: 21-35 days (average: 28 days)
Method 2: Ultrasound Dating
Date of ultrasound examination
Weeks from ultrasound report
Additional days (0-6)
Medical Disclaimer
This calculator provides estimates only. Only about 5% of babies are born exactly on their due date. Normal pregnancy ranges from 37-42 weeks. Always consult your healthcare provider for medical advice and pregnancy monitoring.
Pregnancy Timeline
First Trimester
Weeks 1-13
Organ development begins
Second Trimester
Weeks 14-27
Growth and movement
Third Trimester
Weeks 28-40+
Final development & preparation
Key Milestones
Due Date Facts
Only 5% of babies are born on their exact due date
Most babies are born within 2 weeks of the due date
First babies tend to be born later than subsequent babies
Ultrasound dating is most accurate in the first trimester
Understanding Due Date Calculation Methods
Naegele's Rule (LMP Method)
The traditional method adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14.
EDD = LMP + 280 days
Limitations:
- • Assumes regular 28-day cycles
- • Less accurate for irregular periods
- • May not account for late or early ovulation
Ultrasound Dating Method
Uses fetal measurements to determine gestational age. Most accurate when performed in the first trimester, with accuracy decreasing as pregnancy progresses.
Advantages:
- • More accurate for irregular cycles
- • Based on actual fetal development
- • Can detect multiple pregnancies
- • Can identify potential growth issues
Accuracy by trimester:
- • First trimester: ±3-5 days
- • Second trimester: ±1-2 weeks
- • Third trimester: ±2-3 weeks
When to Redate Pregnancy
Healthcare providers may adjust your due date based on ultrasound findings. The American College of Obstetricians and Gynecologists provides these guidelines for redating:
| Gestational Age | Redate if Difference > |
|---|---|
| < 9 weeks | 5 days |
| 9-15 weeks | 7 days |
| 16-21 weeks | 10 days |
| 22-27 weeks | 14 days |
| > 28 weeks | 21 days |