How to Calculate Your Due Date: Methods & Accuracy
Learn how to accurately calculate your pregnancy due date using different methods, including last menstrual period, conception date, and ultrasound measurements.
Understanding Due Date Calculation
Calculating your due date is one of the first steps in pregnancy planning. While only about 5% of babies are born on their exact due date, having an accurate estimate helps you and your healthcare provider plan for your pregnancy journey.
Get an accurate due date estimate with our Pregnancy Calculator !
Methods to Calculate Due Date
1. Last Menstrual Period (LMP) Method
Calculation: Add 280 days (40 weeks) to the first day of your last period
- Pros: Easy to calculate, widely used
- Cons: Less accurate for irregular cycles
- Accuracy: ±2 weeks
2. Conception Date Method
Calculation: Add 266 days (38 weeks) to the conception date
- Pros: More accurate if conception date is known
- Cons: Conception date often uncertain
- Accuracy: ±2 weeks
3. Ultrasound Method
Method: Measures fetal size to determine gestational age
- Pros: Most accurate method, especially before 12 weeks
- Cons: Requires medical visit
- Accuracy: ±5-7 days (early ultrasound)
Factors Affecting Due Date Accuracy
Calculate Your Due Date
Our Pregnancy Calculator helps you:
- • Get accurate due date estimates
- • Track pregnancy milestones
- • Plan prenatal appointments
- • Monitor fetal development
Important Pregnancy Milestones
First Trimester (Weeks 1-12)
- First ultrasound (6-8 weeks)
- End of highest risk period (12 weeks)
Second Trimester (Weeks 13-26)
- Gender ultrasound (18-22 weeks)
- First felt movements (18-20 weeks)
Third Trimester (Weeks 27-40)
- Viability (24 weeks)
- Full term (37 weeks)
Frequently Asked Questions
Why do doctors add 40 weeks from LMP?
This accounts for the typical 2 weeks before ovulation plus 38 weeks of pregnancy.
What if I have irregular periods?
An early ultrasound will provide the most accurate due date.
How often do babies arrive on their due date?
Only about 5% of babies are born on their exact due date.
Try Our Pregnancy Calculator
Final Thoughts
While due date calculations provide essential estimates, remember they're just predictions. Every pregnancy is unique. Use our pregnancy calculator to get a comprehensive view of your pregnancy timeline and important milestones.
References & Medical Sources
- American College of Obstetricians and Gynecologists (ACOG): Due Date Calculation Methods
- Mayo Clinic: Pregnancy Week by Week
About this Medical Article
Learn how to accurately calculate your pregnancy due date using different methods, including last menstrual period, conception date, and ultrasound measurements.