Gestational Age Calculator
Gestational Age Calculator
Gestational age — the length of time a baby has been developing in the womb — is one of the most critical pieces of information in newborn care. It determines whether a baby is preterm (born before 37 weeks), term (37–41 weeks), or post-term (42 weeks or more). Gestational age affects every aspect of newborn management, from feeding protocols to screening tests to monitoring for complications like respiratory distress, jaundice, and hypothermia.
According to the World Health Organization (WHO), approximately 13.4 million babies were born preterm in 2024. Preterm birth is the leading cause of death in children under 5 worldwide. Accurate gestational age assessment helps clinicians anticipate and prepare for complications, and guides decisions about feeding, temperature regulation, and intensive care needs.
Methods for Determining Gestational Age
- Last Menstrual Period (LMP): The traditional method — counting weeks from the first day of the last menstrual period. This is most accurate when the menstrual history is reliable.
- First-trimester ultrasound: The most accurate method, with an error margin of ±5–7 days. Crown-rump length (CRL) is measured before 14 weeks.
- Newborn Ballard Score: A physical and neurological assessment performed after birth, scoring 12 criteria on a scale of -1 to 5. The total score estimates gestational age within ±2 weeks.
Classification by Gestational Age
- Extremely preterm: Born before 28 weeks
- Very preterm: Born 28 to 32 weeks
- Moderate to late preterm: Born 32 to 37 weeks
- Term: Born 37 to 41 weeks
- Post-term: Born at 42 weeks or more
Gestational Age Calculator
Gestational Age Calculator
Calculate gestational age from the first day of your last menstrual period.
Frequently Asked Questions
What is gestational age?
Gestational age is the duration of pregnancy measured from the first day of the last menstrual period (LMP), expressed in weeks and days. A full-term pregnancy is 37-41 weeks; before 37 weeks is preterm.
Which method is most accurate for dating?
First-trimester ultrasound (crown-rump length before 14 weeks) is the most accurate, with an error of ±5-7 days. LMP-based dating is reliable when menstrual history is regular and certain. For newborns, the Ballard score estimates gestational age clinically.
What are the preterm categories?
Extremely preterm (before 28 weeks), very preterm (28 to 32 weeks), moderate to late preterm (32 to 37 weeks), term (37-41 weeks), and post-term (42 weeks or more).
Why does gestational age matter for newborn care?
It guides feeding plans, screening, and monitoring for complications like respiratory distress, jaundice, hypoglycemia, and temperature instability. Preterm infants have different care needs than term infants.
Authoritative Resources
Written by Dr. Emily Chen, MD (Pediatrics) | Medically approved by Dr. Ahmed Raza, MD (Pediatrics) | Updated for 2026
Disclaimer: This calculator is for general informational purposes only and is not a substitute for professional medical advice. Always consult your pediatrician.
