Corrected Age Calculator

Q: What is the difference between corrected age and chronological age?

Chronological age is calculated from the actual birth date. Corrected age is calculated from the original due date, subtracting weeks of prematurity. For growth charts and developmental milestones, corrected age is more accurate for premature infants.

Q: My baby was born at 36 weeks. Should I use corrected age?

Babies born at 36 weeks are late preterm and were only 4 weeks early. Many pediatricians still recommend correcting for the first 12 months, especially for growth chart percentiles.

Q: How do I use corrected age on growth charts?

Enter your baby's due date as the date of birth in any growth calculator. This automatically applies the correction. Alternatively, calculate the corrected age and enter it directly using the Enter Age option.

Q: Does corrected age apply to developmental milestones?

Yes. Motor and language milestones should be evaluated using corrected age for at least the first 12-18 months. A baby born 2 months early is expected to reach milestones about 2 months later than full-term peers.

Calculate your premature baby's corrected (adjusted) age from their birth date and due date. Use corrected age when plotting growth charts for preterm infants.

By Dysin, software engineer & parent · About & methodology

schedule 3 min read

What is corrected age? Corrected age (also called adjusted age) is your premature baby's age calculated from their due date instead of their birth date. It reflects where they are developmentally — a baby born 8 weeks early who is 6 months old chronologically is about 4 months old in corrected age. Pediatricians use corrected age when plotting growth charts until age 2–3. Learn more in our premature baby growth guide →

Date of Birth

Original Due Date

Calculate Age As Of Defaults to today. Change to check corrected age at a past or future date.

Gestational Age at Birth
Weeks of Prematurity
Chronological Age
Corrected Age

This tool is for informational purposes only and is not a substitute for professional medical advice. Premature infants require close medical follow-up. Always consult your child's pediatrician or neonatologist.

How This Corrected Age Calculator Works

This calculator determines how many weeks early your baby was born and subtracts that time from their chronological age. The formula is straightforward:

Corrected age = Chronological age − Weeks of prematurity

Weeks of prematurity is calculated as 40 weeks minus the gestational age at birth. For example, a baby born at 32 weeks gestation was 8 weeks premature (40 − 32 = 8). If that baby is now 6 months old, their corrected age is approximately 4 months.

Why Corrected Age Matters for Growth Charts

When you plot a premature baby's weight or length on a standard WHO or CDC growth chart, using their birth date makes them appear smaller than they really are. A 6-month-old born at 32 weeks should be compared to 4-month-olds — not other 6-month-olds — because they had 2 fewer months of growth time.

Using chronological age for a preemie often causes unnecessary worry about low percentiles. Corrected age gives you an accurate picture of whether your baby is growing appropriately for their developmental stage.

When to Stop Using Corrected Age

Most pediatricians stop correcting between 24 and 36 months, depending on the degree of prematurity and catch-up progress:

Head circumference: Stop correcting at approximately 18–24 months (catches up earliest)
Weight: Stop correcting at approximately 24 months
Height/length: Stop correcting at approximately 24–36 months

For very early preemies (born before 28 weeks), some clinicians continue correcting until age 3. Your pediatrician will determine the right time based on your baby's individual progress.

Corrected Age and Developmental Milestones

Corrected age also applies to developmental milestones. A baby born 2 months early is expected to reach milestones approximately 2 months later than a full-term baby of the same birth date. Rolling, sitting, crawling, and first words should all be evaluated using corrected age during the first 1–2 years.

Using This Calculator with Our Growth Tools

After calculating your baby's corrected age, use it when entering data in our growth calculators. The easiest method: enter your baby's due date as the "date of birth" in any calculator — this automatically applies the correction. Alternatively, switch to "Enter Age" mode and type the corrected age directly.

Weight-for-Age — track weight percentile using corrected age
Height-for-Age — compare length to corrected-age peers
Head Circumference — monitor brain growth (often catches up first)
Growth Velocity — check if catch-up growth rate is on track
Growth Tracker — log visits over time and visualize the catch-up trajectory

Corrected Age FAQ

What is the difference between corrected age and chronological age?

Chronological age is calculated from your baby's actual birth date. Corrected age is calculated from the original due date, subtracting the weeks of prematurity. For growth charts and developmental milestones, corrected age is more accurate for premature infants because it reflects their true developmental stage.

My baby was born at 36 weeks. Should I use corrected age?

Babies born at 36 weeks are considered "late preterm" and were only 4 weeks early. While correction is less critical than for earlier preemies, many pediatricians still recommend correcting for the first 12 months — especially when evaluating growth chart percentiles. Ask your pediatrician whether correction is appropriate for your baby.

How do I use corrected age on growth charts?

The simplest method is to enter your baby's due date as the "date of birth" in any of our growth calculators. This automatically applies the correction. Alternatively, calculate the corrected age here and enter it directly using the "Enter Age" option on any calculator.

Does corrected age apply to developmental milestones?

Yes. Motor milestones (rolling, sitting, crawling, walking) and language milestones should be evaluated using corrected age for at least the first 12–18 months. A baby born 2 months early is expected to reach milestones approximately 2 months later than full-term peers. Use our Milestone Tracker with corrected age for a more accurate assessment.

When do premature babies catch up in growth?

Most preterm babies achieve catch-up growth by age 2–3. Head circumference typically catches up first (6–12 months corrected age), followed by weight (12–24 months), and finally length (up to 3 years). About 80–90% of preterm infants reach the normal range by corrected age 2–3. Read more in our premature baby growth guide.

Can a baby have a negative corrected age?

Yes. If your baby was born very early and is still before their original due date, their corrected age is negative — meaning they haven't yet reached "term equivalent" age. For example, a baby born at 28 weeks who is now 2 weeks old chronologically has a corrected age of approximately −10 weeks. Growth during this period is typically monitored using Fenton preterm charts in the NICU.