Gestational Age Calculator Baby Center

Tracking your baby's gestational age is essential for monitoring pregnancy progress. This calculator helps you determine your baby's age based on your last menstrual period (LMP) or ultrasound date. Understanding gestational age provides insight into fetal development stages and helps prepare for your baby's arrival.

What is Gestational Age?

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

The average pregnancy lasts about 40 weeks (280 days). Gestational age is divided into trimesters:

First trimester: Weeks 1-12
Second trimester: Weeks 13-28
Third trimester: Weeks 29-40

Tracking gestational age helps healthcare providers monitor fetal development, assess growth, and identify any potential issues.

How to Use This Calculator

To calculate your baby's gestational age:

Select whether you want to calculate from your last menstrual period (LMP) or from an ultrasound date.
Enter the relevant date (LMP date or ultrasound date).
Enter today's date.
Click "Calculate" to see your baby's gestational age.

Note: For most accurate results, use the date of a confirmed ultrasound rather than estimating from your LMP.

Gestational Age Formula

The gestational age is calculated by determining the number of weeks and days between the reference date (LMP or ultrasound) and today's date.

Gestational Age = (Today's Date - Reference Date) / 7 days per week

For example, if today is 30 days after your LMP, your baby's gestational age would be:

30 days / 7 days per week = 4.285 weeks

4 weeks + 0.285 weeks × 7 days per week ≈ 4 weeks and 2 days

Gestational Age Chart

The following chart shows typical fetal development stages at different gestational ages:

Gestational Age	Development Stage
Weeks 1-4	Implantation and early organ formation
Weeks 5-8	Major organs forming, limbs developing
Weeks 9-12	Facial features developing, movement possible
Weeks 13-16	Hair, nails, and skin forming, baby can hear
Weeks 17-20	Eyes open, baby can taste, hair growing
Weeks 21-24	Lungs developing, baby can swallow
Weeks 25-28	Skin becomes less transparent, baby can dream
Weeks 29-32	Fat deposits forming, baby can hear outside sounds
Weeks 33-36	Bones hardening, baby gains weight rapidly
Weeks 37-40	Full-term baby, ready for birth

FAQ

How accurate is the gestational age calculator?: The calculator provides an estimate based on the dates you enter. For the most accurate results, use the date of a confirmed ultrasound rather than estimating from your last menstrual period.
What if my due date is different from the calculator's result?: If your healthcare provider has calculated a different due date, they may have used additional factors such as fetal growth measurements or early ultrasound dates. Always consult with your healthcare provider for personalized advice.
When should I see a doctor about my baby's gestational age?: If your baby's gestational age is significantly different from what was expected (either ahead or behind schedule), contact your healthcare provider immediately. They can monitor your baby's growth and development.
Can I use this calculator for multiple pregnancies?: This calculator is designed for single pregnancies. For multiple pregnancies, you should use the specific calculations provided by your healthcare provider.