Pregnancy Calculator
Calculate your due date, track pregnancy weeks, and get week-by-week fetal development information. Our pregnancy calculator helps you plan and monitor your pregnancy journey.
How the Pregnancy Calculator Works
Understanding pregnancy calculations and important milestones
Calculating Your Due Date
Pregnancy is typically calculated from the first day of your last menstrual period (LMP), even though conception usually occurs about two weeks later. This method is used because most people know when their last period started, but not when they ovulated.
Naegele’s Rule
The standard method for calculating due dates is Naegele’s Rule:
- Start with the first day of your last menstrual period
- Add 7 days
- Subtract 3 months
- Add 1 year
For example: LMP = October 1, 2023 → Due Date = July 8, 2024
Important Considerations
- Only about 5% of babies are born on their exact due date
- Most births occur within two weeks before or after the due date
- Your healthcare provider may adjust your due date based on ultrasound measurements
- IVF pregnancies have more precise dating based on transfer date
Pregnancy Trimesters
First Trimester
Weeks 1-13
- Major organ development
- Morning sickness common
- Fatigue and breast tenderness
- First ultrasound around week 8-12
Second Trimester
Weeks 14-27
- Baby’s movements felt
- Anatomy scan around week 20
- Energy typically returns
- Baby’s sex can be determined
Third Trimester
Weeks 28-40+
- Rapid weight gain
- Baby positions for birth
- Braxton Hicks contractions
- Final preparations for delivery
Week-by-Week Fetal Development
Track your baby’s growth and development throughout pregnancy
Week 12 Development
Baby’s Size
About the size of a plum, measuring approximately 2.1 inches (5.4 cm) and weighing 0.49 ounces (14 grams).
Key Developments
Reflexes are developing, fingers and toes have separated, and bones are beginning to harden. The baby can make sucking movements.
Mom’s Changes
Morning sickness may start to improve, energy levels might increase, and the uterus is growing above the pelvic bone.
Track Your Pregnancy Journey
Use our comprehensive health calculators to monitor your pregnancy and make informed decisions about your health and your baby’s development.
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