Due Date Calculator: Your Complete Guide to Pregnancy Timeline
👶 Planning Your Pregnancy Journey?
Our medically-reviewed Due Date Calculator combines advanced calculation methods with expert guidance to give you a precise estimate of your baby's arrival. Whether you're newly pregnant or planning ahead, we provide comprehensive week-by-week insights backed by the latest obstetric research.
Understanding Your Due Date: The Science Behind the Calculation
How We Calculate Your Due Date
From Last Menstrual Period (LMP)
Naegele's Rule: Add 1 year, subtract 3 months, and add 7 days to the first day of your last period. This method assumes a 28-day cycle with ovulation on day 14.
From Conception Date
Add 266 days (38 weeks) to the estimated date of conception. More accurate if you know when conception occurred, such as with IVF.
🔍 Scientific Accuracy
Research shows that only about 4% of babies are born on their exact due date, with 90% arriving within two weeks before or after. Factors like first-time pregnancy and family history can influence timing.
Your Pregnancy Timeline: Week-by-Week Development
First Trimester (Weeks 1-12)
Weeks 1-4: Early Development
- Fertilization and implantation occur
- Pregnancy hormone (hCG) becomes detectable
- Neural tube begins forming
Weeks 5-8: Critical Formation
- Major organs begin developing
- Heart starts beating
- Facial features form
Weeks 9-12: Rapid Growth
- Baby's length doubles
- External genitalia begin forming
- Movement begins (though not yet felt)
Second Trimester (Weeks 13-26)
Weeks 13-16: Visible Changes
- Gender becomes visible on ultrasound
- Fingerprints and toenails form
- Baby begins making sucking motions
Weeks 17-20: Movement Milestone
- First movements felt ("quickening")
- Detailed anatomy scan performed
- Baby can hear sounds
Weeks 21-26: Continued Growth
- Regular movement patterns develop
- Taste buds form
- Sleep cycles establish
Third Trimester (Weeks 27-40+)
Weeks 27-31: Rapid Development
- Brain growth accelerates
- Eyes can open and close
- Immune system strengthens
Weeks 32-36: Final Preparations
- Lungs mature
- Baby moves into head-down position
- Fat layers develop
Weeks 37-40+: Ready for Birth
- Full-term development reached
- Final weight gain occurs
- Position settles for delivery
Essential Prenatal Care Timeline
First Trimester Checklist
- ✓Weeks 4-8:
First prenatal visit, blood tests, medical history
- ✓Weeks 10-12:
Genetic screening, ultrasound for dating
Second Trimester Checklist
- ✓Weeks 18-22:
Anatomy scan, gender reveal (if desired)
- ✓Weeks 24-28:
Glucose screening, vaccines, RhoGAM if needed
Third Trimester Checklist
- ✓Weeks 32-36:
Group B strep test, growth scans, birth plan review
- ✓Weeks 36-40:
Weekly checks, position check, labor signs review
Expert Insights: Common Questions Answered
How accurate is my due date?
According to the American College of Obstetricians and Gynecologists (ACOG):
- Only 1 in 25 babies arrives on their exact due date
- First-time mothers often deliver 5-7 days late
- Ultrasound dating in the first trimester is most accurate (±5 days)
What affects my due date?
Medical Factors
- Previous pregnancy history
- Maternal age and health
- Fertility treatments used
- Multiple pregnancies
Lifestyle Factors
- Stress levels
- Physical activity
- Nutrition and weight
- Work environment
Preparing for Labor: Know the Signs
Early Labor Signs
- Braxton Hicks contractions
- Lightening (baby drops lower)
- Increased back pain
- Mild cramping
Active Labor Signs
- Regular, strong contractions
- Water breaking
- Bloody show
- Intense pressure
🚨 When to Call Your Doctor Immediately:
- Severe abdominal pain
- Heavy bleeding
- Decreased fetal movement
- Severe headache or vision changes
- Contractions before 37 weeks
Hospital Bag Checklist
For Mom
- Comfortable nightgown/robe
- Nursing bras
- Toiletries
- Phone charger
- Insurance cards
- Birth plan copies
For Baby
- Diapers and wipes
- Going home outfit
- Blankets
- Car seat
- Socks/mittens
- Hat
For Partner
- Change of clothes
- Snacks and drinks
- Camera
- Toiletries
- Entertainment items
- Important contacts list