Due Date Calculator
Calculate your pregnancy due date and track important milestones. Multiple calculation methods available.
Standard cycle is 28 days
Medical Disclaimer: This calculator provides estimates only and should not replace professional medical advice. Always consult with your healthcare provider for accurate dating and prenatal care.
Quick Answer
Pregnancy typically lasts 40 weeks (280 days) from the first day of your last menstrual period. Use your LMP date for the most common calculation method, or use conception date, IVF transfer date, or ultrasound measurements for more specific estimates.
Dr. Snezana Lawrence
Mathematical Historian
15+ years experience
PhD from Yale University. Published mathematical historian ensuring precision in all calculations.
Education
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Table of Contents
Calculation Methods Explained
Last Menstrual Period (LMP)
The most common method uses Naegele's rule: add 280 days to the first day of your last period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the calculation adjusts accordingly.
Conception Date
If you know when you conceived, this method adds 266 days (38 weeks) from conception. This is more accurate if you tracked ovulation or know the exact conception date.
IVF Transfer Date
For IVF pregnancies, the calculation is based on the embryo transfer date and embryo age. Day 3 embryos add 263 days, while Day 5 (blastocyst) embryos add 261 days.
Ultrasound Measurement
Early ultrasounds can accurately measure gestational age. If you know the gestational age at a specific ultrasound date, the due date is calculated from those measurements.
Understanding Pregnancy Dates
Pregnancy dating can be confusing because it's counted from the LMP, not conception:
- Gestational Age: Counted from LMP (40 weeks total)
- Fetal Age: Counted from conception (38 weeks total)
- Weeks 1-2: Before conception actually occurs
- Week 3: Fertilization and implantation
- Week 4: First missed period typically occurs
The Three Trimesters
First Trimester
Weeks 1-13
- Major organs form
- Morning sickness common
- Highest miscarriage risk
Second Trimester
Weeks 14-27
- Baby movements felt
- Gender can be determined
- Energy often returns
Third Trimester
Weeks 28-40
- Rapid baby growth
- Preparation for birth
- More frequent checkups
Accuracy of Due Date Estimates
Due dates are estimates, not guarantees. Here's what the statistics show:
- Only about 5% of babies are born on their due date
- About 80% of babies are born within 2 weeks of the due date
- Full term is considered 37-42 weeks
- First-time mothers often deliver 1-2 weeks late
- Early ultrasound dating is most accurate (±5-7 days)
Frequently Asked Questions
How accurate is a due date calculator?
Due date calculators provide estimates. Only about 5% of babies are born on their exact due date. Most babies are born within 1-2 weeks before or after the estimated date. First-trimester ultrasound dating is typically the most accurate method.
What is Naegele's rule?
Naegele's rule is the standard method for calculating due dates. It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14.
How is pregnancy counted - from conception or LMP?
Pregnancy is conventionally counted from the first day of your last menstrual period (LMP), not from conception. This means when you're "4 weeks pregnant," conception actually occurred about 2 weeks ago.
Can my due date change?
Yes, your due date may be adjusted based on ultrasound measurements, especially if they differ significantly from LMP-based calculations. Early ultrasounds (before 12 weeks) are most accurate for dating.
What if I have irregular periods?
If you have irregular periods, LMP-based calculations may be less accurate. In this case, an early ultrasound is the best way to determine gestational age and estimate your due date.
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Dr. Snezana Lawrence
Mathematical Historian | PhD from Yale
Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.
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