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Calculate Baby Age in Womb

Reviewed by Calculator Editorial Team

Understanding your baby's age in the womb is crucial for tracking pregnancy progress. This calculator helps you determine your baby's gestational age based on your last menstrual period (LMP) or ultrasound date.

What is Gestational Age?

Gestational age refers to the length of time a baby has been developing in the womb, measured in weeks and days. It's typically calculated from the first day of the last menstrual period (LMP) or from the date of a confirmed ultrasound.

The average pregnancy lasts about 40 weeks (280 days), but gestational age can vary. Early pregnancy is considered up to 13 weeks, the second trimester runs from 14 to 27 weeks, and the third trimester begins at 28 weeks.

How is Baby Age Measured?

There are two primary methods to determine gestational age:

  1. Last Menstrual Period (LMP): Counting from the first day of your last menstrual period. This method is less precise because menstrual cycles vary.
  2. Ultrasound: The most accurate method, where an ultrasound measures the baby's crown-rump length (CRL) or biparietal diameter (BPD).

Our calculator uses both methods to provide an accurate estimate of your baby's age in the womb.

Important Milestones

Each week of pregnancy brings new developments. Here are some key milestones:

  • Weeks 1-4: Implantation and early organ formation
  • Weeks 5-8: Major organs begin to develop, heart starts beating
  • Weeks 9-12: Limbs and digits form, baby can hear sounds
  • Weeks 13-16: Baby can make facial expressions, eyelids open
  • Weeks 17-20: Baby can suck thumb, hair starts growing
  • Weeks 21-24: Baby can hear outside sounds, practice breathing
  • Weeks 25-28: Baby's skin becomes less transparent, can taste
  • Weeks 29-32: Baby gains weight rapidly, prepares for birth
  • Weeks 33-36: Baby is in "active survival mode," practicing breathing
  • Weeks 37-40: Baby is considered full-term, ready for birth

Pregnancy Weeks Chart

The following table shows key developments during each week of pregnancy:

Week Development
1-4 Implantation, early organ formation
5-8 Heart begins to beat, major organs develop
9-12 Limbs and digits form, baby can hear sounds
13-16 Eyelids open, baby can make facial expressions
17-20 Baby can suck thumb, hair starts growing

FAQ

How accurate is the gestational age calculator?
The calculator provides an estimate based on your last menstrual period or ultrasound date. For the most accurate results, consult with your healthcare provider.
What if my LMP and ultrasound dates don't match?
If there's a discrepancy between your LMP and ultrasound dates, the ultrasound measurement is typically more reliable. Your healthcare provider can help interpret these differences.
When should I get an ultrasound to confirm my baby's age?
Most healthcare providers recommend an ultrasound between 11-14 weeks of pregnancy to confirm your due date and assess your baby's development.
What counts as a full-term pregnancy?
A full-term pregnancy is generally considered to be 37-42 weeks. Babies born between 37-40 weeks are considered full-term, while those born between 41-42 weeks are considered post-term.