How do you calculate corrected age?

Subtract the number of weeks your baby was born early from their actual age. Weeks early = 40 minus gestational age at birth.

What is the difference between corrected age and actual age?

Actual age counts from the birth date. Corrected age counts from the due date, so it's younger for a premature baby.

When do you stop using corrected age?

Usually around 2 years, sometimes up to 3 for very premature babies, according to the AAP. Your pediatrician will advise.

Should vaccines follow corrected age?

Generally no. Vaccines are usually given by actual age, but follow your baby's care team.

Is corrected age needed for a baby born at 37 weeks?

No. Babies born at 37 weeks or later are full term, so actual age is used.

Corrected Age Calculator for Preemies / Tot

Medically reviewed by Safi Ullah Khan · Written by Muneeb Rana · Last updated 21 October 2026

Quick answer: A corrected age calculator subtracts how early your baby was born from their actual age. Corrected age = age since birth minus (40 weeks minus gestational age at birth). A 6-month-old born at 32 weeks is 8 weeks early, so their corrected age is about 4 months. The AAP uses it until about age 2-3.

TL;DR

Enter birth date and gestational age at birth (weeks + days).
Corrected age is used for milestones and growth, not for vaccines.
Most children catch up by 2-3 years; ask your pediatrician when to stop.

This corrected age calculator shows a premature baby's actual (chronological) age and corrected (adjusted) age side by side. Corrected age is what pediatricians use to judge development and growth for babies born before 37 weeks, so a 'late' milestone isn't misread.

How to use the corrected age calculator

Enter your baby's birth date.
Enter gestational age at birth in weeks and days (from your discharge papers).
Read actual age, weeks early and corrected age in weeks and months.
Use corrected age with the milestone checker and growth percentile calculator.
Use actual age for the vaccine schedule unless your care team says otherwise.

How the corrected age calculator works

weeks_early   = 40 - gestational_age_at_birth
corrected_age = actual_age - weeks_early
if gestational_age_at_birth >= 37 weeks: corrected age is not needed

Born at	Weeks early	Actual age 6 months → corrected
36 weeks	4	about 5 months
32 weeks	8	about 4 months
28 weeks	12	about 3 months
26 weeks	14	about 2.5 months

Worked example

Zara was born at 30 weeks + 2 days on 1 March 2026. On 21 October 2026 her actual age is 33 weeks (about 7.5 months). She was 9 weeks 5 days early, so her corrected age is about 23 weeks, or 5 months 1 week. Her parents use the 4- and 6-month milestone lists, not the 6- and 9-month ones.

What corrected age is used for

The AAP explains that preemies should be compared with babies born at the same time from their due date, not their birth date, for development and growth. Sleep and feeding expectations often follow corrected age too. Vaccines are usually given by actual age; your care team will confirm.

When to stop correcting

The AAP says most preemies catch up by 2 to 3 years, and many pediatricians stop correcting around age 2. Very premature babies may be followed for longer.

Preterm babies and feeding plans

Many preterm babies go home with a specific feeding plan. Follow it rather than general charts, and log feeds in Tot so your neonatal or pediatric team sees the full picture. NICHD has background on preterm birth. See also the baby age calculator.

Download Tot free on the App Store or Google Play. Free with ads; optional Premium.

Sources

AAP HealthyChildren.org: Corrected Age for Preemies: www.healthychildren.org (accessed 21 October 2026)
NICHD: Preterm labor and birth: www.nichd.nih.gov (accessed 21 October 2026)
CDC: Developmental Milestones (Learn the Signs. Act Early.): www.cdc.gov (accessed 21 October 2026)
WHO: Child Growth Standards: www.who.int (accessed 21 October 2026)

Medical disclaimer:

Tot and this website give general information only. Feeding, sleep and growth ranges vary; always follow your pediatrician's advice. If your baby is unwell, contact your doctor or emergency services.

Corrected Age Calculator for Premature Babies