Preterm · 0–24 months Evidence-based Free & private

Corrected Age Calculator for Premature Babies

Calculate adjusted (corrected) age for babies born preterm. Used to interpret growth, milestones, and screening tools accurately until 24 months.

Start calculating Learn about Corrected Age Calculator for Premature Babies
Preterm baby cradled inside a glowing mint heart in a NICU setting
Category
Development
Trust
Medical-grade

Weeks (20–42)

Days (0–6)

Enter date of birth and gestational age at birth to calculate corrected age.
Medically reviewed by ASQCalculator Editorial Team
Last reviewed: June 25, 2026Review policyMethodology

Understanding this tool

Plain-language explanations grounded in current pediatric evidence.

TL;DR

Corrected age subtracts the weeks your baby was born early from their chronological age. Use it for growth charts, milestones, and developmental screeners (including ASQ-3) until 24 months — but use chronological age for vaccinations.

What it is

Corrected age (also called adjusted age) accounts for the weeks a baby was born early. It's the age your baby would be if they had been born on their due date.

How it's calculated

Corrected age = chronological age − (40 weeks − gestational age at birth). Example: a 6-month-old born at 32 weeks has 8 weeks subtracted, giving a corrected age of about 4 months.

When to use it

Use corrected age for growth percentiles, developmental screening (including ASQ-3), and milestone expectations until the child reaches 24 months of corrected age.

Who should use it

Pediatricians, neonatologists, NICU follow-up clinics, parents of preterm infants, early intervention therapists.

Clinical importance

Using chronological age for a preterm baby leads to over-referral for "developmental delay" and inaccurate growth interpretation. The AAP recommends correcting for prematurity until age 2.

Example

A baby born on 1 Jan 2025 at 30 weeks 0 days was 10 weeks premature. On 1 Jul 2025 their chronological age is 6 months but their corrected age is about 4 months.

How to use this calculator

  1. 1
    Enter date of birth
    Pick your baby's actual birth date.
  2. 2
    Enter gestational age at birth
    Weeks (20–42) and days (0–6) at delivery — find this on the discharge summary.
  3. 3
    Pick a reference date
    Defaults to today; change to project a future age.
  4. 4
    Read both ages
    Use corrected age for growth charts and milestones, chronological age for vaccines.
  5. 5
    Stop at 24 months corrected
    Most clinicians stop adjusting once corrected age reaches 24 months.

Common mistakes to avoid

  • Subtracting weeks from the wrong direction — the correction reduces age, not adds.
  • Continuing to correct after 24 months of corrected age.
  • Using corrected age for vaccination schedules (use chronological).
  • Forgetting the days component of gestational age (e.g. 32w 4d, not just 32w).
  • Not re-checking the questionnaire interval after correction (it may shift you to a different ASQ-3 form).

Glossary

Gestational age (GA)
Weeks of pregnancy completed at birth; full-term is 37–41 weeks.
Preterm
Born before 37 completed weeks of gestation.
Corrected / adjusted age
Age based on the expected due date rather than the actual birth date.
NICU follow-up
Specialty clinic that tracks growth and development of preterm or critically ill newborns.

Medical references

Frequently asked questions

Answers parents and pediatric professionals ask most often about this tool.

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Medical disclaimer. This calculator is an educational tool and does not replace evaluation by a qualified pediatric clinician. If you are concerned about your child's development or health, contact your pediatrician.