Due Date Calculator - When is My Baby Due? | HealthCalc
Calculate your probable due date using Naegele's rule. Discover how many weeks pregnant you are and important pregnancy milestones.
Due Date Calculator
Calculate your probable due date and current weeks of pregnancy
Naegele's Rule
The probable due date is calculated by adding 280 days (40 weeks) to the date of the last period.
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What is Naegele's Rule?
Naegele's Rule is a standard method used in obstetrics to calculate the probable due date (EDD). It was developed by German obstetrician Franz Karl Naegele in the 19th century and is still widely used today.
The rule states that pregnancy lasts approximately 280 days (40 weeks) from the first day of the last menstrual period (LMP).
Naegele's Formula:
Probable Due Date = First day of last menstrual period + 280 days
Or equivalently: EDD = LMP + 7 days + 9 months
Pregnancy Trimesters
Pregnancy is traditionally divided into three trimesters, each with unique characteristics and developments:
First Trimester (Weeks 1-13)
Key development: Formation of major organs, nervous system, heart, and baby's limbs.
Common experiences: Nausea, fatigue, hormonal changes, breast tenderness, mood swings.
Second Trimester (Weeks 14-27)
Key development: Rapid growth, movement development, facial feature formation, sensory organ development.
Common experiences: Increased energy, first perception of baby movements (around week 18-20), more visible belly growth.
Third Trimester (Weeks 28-40)
Key development: Significant weight gain, lung and organ maturation, subcutaneous fat development, preparation for birth.
Common experiences: Increased discomfort, difficulty sleeping, Braxton Hicks contractions, preparation for labor.
Why is the Due Date "Probable"?
It's important to understand that the calculated date is an estimate, not an exact date. Statistics show that:
- • Only approximately 5% of babies are born on the exact calculated date
- • Most babies are born between 2 weeks before and 2 weeks after the probable date (weeks 38-42)
- • Births between weeks 37-42 are considered full term
Factors that can affect the due date:
- • Variations in menstrual cycle length
- • Accuracy of memory of last menstruation
- • Genetic and family factors
- • Number of previous pregnancies
- • Maternal or baby medical conditions
Important Milestones During Pregnancy
Week 12
End of first trimester. Significant reduction in miscarriage risk. Possibility of performing ultrasound and seeing the baby.
Week 18-20
Detailed anatomical ultrasound. First perception of baby movements (especially in first-time mothers).
Week 24
Baby viability. Babies born after this week have survival chances with intensive care.
Week 28
Start of third trimester. Baby's lungs begin to mature. Increase in prenatal visits.
Week 37
Considered early full term. Baby is fully developed and can be born at any time.
Week 40
Calculated probable due date. Most babies are born before or after this date.
Birth Classification by Gestation Time
Preterm (Before week 37)
Babies born before 37 completed weeks. Require special care depending on the week of birth.
Full Term (Weeks 37-42)
Considered the optimal range for birth. Organs are fully developed and baby is ready for life outside the uterus.
Post-term (After week 42)
Pregnancies that extend beyond 42 weeks. May require additional monitoring and possibly labor induction.
Important Considerations
- ⚠ Irregular cycles: If your menstrual cycle is irregular or you don't remember the exact date of your last period, the calculator may be less accurate. Consult with your obstetrician for a more accurate estimate through ultrasound.
- ⚠ Early ultrasound: An ultrasound performed in the first trimester (weeks 6-12) can provide a more accurate estimate of the due date based on baby's size.
- ⚠ Medical follow-up: It's essential to have regular medical follow-up during pregnancy. Your obstetrician will adjust the due date according to the baby's development in ultrasounds.
- ⚠ Normal variations: It's completely normal for the baby to be born before or after the calculated date. Most pregnancies have natural variations.
Urgent Medical Consultation
Seek immediate medical attention if you experience:
- Vaginal bleeding
- Regular contractions before week 37
- Membrane rupture (water breaking)
- Intense abdominal pain
- Decrease in baby movements
- Signs of preeclampsia (high blood pressure, swelling, severe headache)
Medical Disclaimer
This due date calculator is for informational and educational purposes only. It should not be considered medical advice or replace prenatal follow-up with an obstetrician or health professional. The calculated date is an estimate based on Naegele's rule and may vary significantly according to individual factors. It's essential to have regular medical follow-up during pregnancy to monitor baby's development and adjust the due date as necessary through ultrasounds and clinical evaluation.