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Corrected Age Calculator
For babies born before 37 weeks: the corrected age counted from the due date, side by side with chronological age, weeks born early and postmenstrual age.
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A corrected age calculator finds a premature baby's age counted from the due date instead of the birth date. Enter your baby's date of birth, the gestational age at the time of birth (or the due date) and the date of the check-up, and the calculator returns the corrected age in years, months and days.
Each calculation gives 5 results: corrected age, chronological age, weeks born early, the due date and postmenstrual age (PMA). The calculator is for babies born before the 37th week of pregnancy. Parents use it to read milestone charts, and pediatricians, physicians, neonatal intensive care unit (NICU) nurses, physical therapists and speech-language pathologists use it before developmental screening. The same tool goes by 4 other names: adjusted age calculator, premature age calculator, preemie age calculator and corrected gestational age calculator.
What Is Corrected Age?
Corrected age is a premature baby's age counted from the date the baby was due, not the date the baby was born. A full-term pregnancy lasts 40 weeks (280 days) from the first day of the last menstrual period, so a baby born at 32 weeks arrived 8 weeks early and is 8 weeks younger by corrected age than by the calendar.
Corrected age and adjusted age are 2 names for one measure. A preterm baby has 4 ages on a clinic letter, shown here for a baby born on 10 January 2026 at 30 weeks and 2 days and seen on 30 October 2026.
Gestational age
30 wk 2 d
Weeks of pregnancy at birth. Fixed for life.
Chronological age
0;9;20
Time since birth. Used for vaccines, school and legal records.
Corrected age
0;7;11
Time since the due date. Used for milestones and growth.
Postmenstrual age
72 wk 1 d
Gestational age plus time since birth. Used in the NICU.
Which babies need a corrected age
| Born at | Category | Weeks early | Correct the age? |
|---|---|---|---|
| Before 28+0 | Extremely preterm | More than 12 | Yes |
| 28+0 to 31+6 | Very preterm | 8+1 to 12 | Yes |
| 32+0 to 36+6 | Moderate to late preterm | 3+1 to 8 | Yes |
| 37+0 to 38+6 | Early term | 1+1 to 3 | No |
| 39+0 to 40+6 | Full term | 0 to 1 | No |
| 41+0 and later | Late term, post-term from 42+0 | None | No |
The World Health Organization (WHO) defines preterm birth as birth before 37 completed weeks and splits it into the 3 preterm groups. The American College of Obstetricians and Gynecologists (ACOG) names the 4 term groups from 37 weeks on. Weeks are written as weeks+days, so 31+6 means 31 weeks and 6 days.
How to Use the Corrected Age Calculator
To use the corrected age calculator, enter your baby's date of birth, add the gestational age at birth or the due date, set the assessment date and press Calculate. The process takes 4 steps.
- Date of birth01/10/2026Enter your baby's date of birth.
Use the date on the birth record. The calculator keeps it in this browser for your next visit.
- Gestational ageDue date30 wk + 2 dAdd the gestational age or due date.
Type weeks plus days, such as 30 + 2, or switch to Due date and enter the date from the dating scan.
- Assessment date today10/30/2026Set the assessment date.
The field starts at today. Change it to the day of the clinic visit, screening or therapy session.
- Corrected age 0;7;11PMA 72 wk 1 dRead the 5 results.
Corrected age leads, with chronological age, weeks early, due date and postmenstrual age below. Copy result puts all of them on the clipboard.
The calculator flags 2 cases where correction usually stops: babies born at 37 weeks or later, and children past 24 months of chronological age. Everything runs in your browser and nothing is uploaded.
Step-by-Step Corrected Age Calculation
To calculate corrected age step by step, find how many weeks early the baby was born, add that gap to the birth date to get the due date, and count the baby's age from the due date. The worked example below uses a baby born on 10 January 2026 at 30 weeks and 2 days and checked on 30 October 2026.
weeks early = 40 weeks − gestational age at birth
due date = date of birth + weeks early
corrected age = assessment date − due date
= chronological age − weeks early
postmenstrual = gestational age at birth + time since birth- Step 1 · Weeks early
40+0 − 30+2
9 wk 5 d= 68 days early - Step 2 · Due date
10 January 2026 + 68 days
19 March 2026the day corrected age starts - Step 3 · Chronological age
10 January 2026 → 30 October 2026
0;9;20293 days since birth - Step 4 · Corrected age
19 March 2026 → 30 October 2026
0;7;11225 days since the due date
The same baby, 2 ways
30 weeks and 2 days is 212 days of pregnancy, and 280 − 212 = 68 days early. Postmenstrual age adds the same 293 days to 30 weeks 2 days, which gives 72 weeks 1 day. Subtract 40 weeks from a postmenstrual age to get the corrected age in weeks.
2 clocks: from birth and from the due date
Chronological age starts at birth. Corrected age starts at the due date, 40 weeks into the pregnancy. The shaded gap is how early the baby arrived. Drag the slider to change the gestational age and watch the corrected age shrink or grow.
Why Is Corrected Age Important for Premature Babies?
Corrected age is important for premature babies for 1 reason: it compares a preterm baby with babies at the same stage of development, not babies with the same birthday. A baby born 10 weeks early spent those 10 weeks in a NICU instead of the womb. Judged by birth date, that baby's normal progress looks like a delay, and parents worry for nothing.
The earlier the birth, the bigger the gap. The chart shows the corrected age of babies who are all 12 months old by the calendar.
12 months old by the calendar: corrected age by gestational age at birth
Corrected age has 8 uses in the first 2 years, including motor skills, growth charts and developmental screening.
Motor skills
Rolling, sitting and walking are checked at corrected age. A 9-month-old born 12 weeks early is expected to move like a 6-month-old.
Language development
Cooing, babbling and first words follow corrected age in the first 2 years.
Social milestones
The first social smile is a 2-month CDC milestone, counted 2 months after the due date for a preemie.
Developmental screening
ASQ-3 uses adjusted age for babies born 3 or more weeks early and under 24 months old.
Physical growth
Weight, length and head circumference go on growth charts at corrected age after the due date.
Feeding milestones
Solid foods start by corrected age plus readiness signs, not by the birth date.
Vision screening
Retinopathy of prematurity (ROP) exams for babies born at 30 weeks or earlier start at 31 weeks PMA or 4 weeks after birth, whichever is later.
Early intervention
Therapists in early intervention record both ages and set goals against corrected-age norms.
Before the due date
- Corticosteroid injections for the mother before an early birth speed up the baby's lung development
- The Apgar score rates the newborn at 1 and 5 minutes after birth
- Head ultrasound scans look through the fontanelles, the soft spots of the skull
- Hyperbilirubinemia (newborn jaundice) lasts longer in preterm babies and gets checked often
After the due date
- Corrected age starts at 0;0;0
- Milestones and growth follow corrected age
- Vaccines stay on chronological age
- Follow-up clinics, hearing checks and eye exams follow the NICU discharge plan
How Long Should You Use Corrected Age?
Use corrected age until your child is 24 months (2 years) old. By 2 years, a gap of a few weeks is small next to the child's whole age, and most preterm children are followed by chronological age from then on. Clinics use 2 cut-offs, and the timeline shows both for a baby born at 28 weeks (12 weeks early).
When correction starts and stops, baby born at 28 weeks
Axis: chronological age in months. For a baby born at 28 weeks, corrected age reaches 24 months at a chronological age of 2;2;24, about 26.8 months after birth.
The gap shrinks every month
The share of life that an 8-week gap takes up for a baby born at 32 weeks, by chronological age.
Who decides
Your pediatrician, the NICU follow-up clinic or a maternal child health nurse tells you which cut-off your clinic follows, and whether to keep correcting adjusted age after NICU discharge past 2 years. Twins and triplets share 1 gestational age, so every baby from the same birth has the same corrected age.
In Australia, the Pregnancy, Birth and Baby helpline connects parents with a maternal child health nurse on 1800 882 436, 7am to midnight (AET), 7 days a week.
Common Mistakes When Calculating Corrected Age
There are 6 common mistakes when calculating corrected age, including counting from 9 months instead of 40 weeks, correcting vaccine dates and correcting babies born at term.
Counting from 9 months
✕ "Full term is 9 months" (about 39 weeks)
✓ Subtract from 40 weeks (280 days)
Dropping the extra days
✕ Entering 30 weeks for a baby born at 30+5
✓ 30+5 means 9 weeks 2 days early, not 10 weeks
Correcting term babies
✕ Correcting a baby born at 38 weeks
✓ Correct only babies born before the 37th week
Correcting vaccines
✕ Delaying 2-month vaccines to 2 months corrected
✓ Vaccinate by chronological age, as the CDC advises
Reading PMA as age
✕ Reading 44 weeks PMA as 44 weeks old
✓ 44 weeks PMA = 4 weeks corrected age
Using the wrong due date
✕ A due date guessed from the last period alone
✓ The due date confirmed by the dating ultrasound
Frequently Asked Questions
How Do I Calculate My Premature Baby's Corrected Age?
To calculate your premature baby's corrected age, subtract the number of weeks your baby was born early from your baby's chronological age. Weeks early equal 40 weeks minus the gestational age at birth. A baby born on 10 January 2026 at 30 weeks and 2 days arrived 9 weeks 5 days early, so on 30 October 2026 the chronological age of 0;9;20 becomes a corrected age of 0;7;11. Enter your baby's date of birth, gestational age and the assessment date in the calculator above to skip the arithmetic.
What Is the Formula for Corrected Age?
The formula for corrected age is chronological age minus (40 weeks − gestational age at birth). Written in days, corrected age = days since birth − (280 − gestational age in days). Counting forward from the due date gives the same answer: corrected age = assessment date − due date.
Is Corrected Age the Same as Adjusted Age?
Yes, corrected age is the same as adjusted age. Both terms mean a premature baby's age counted from the due date. HealthyChildren.org, the parent site of the American Academy of Pediatrics (AAP), says "corrected age", and the Ages & Stages Questionnaires, Third Edition (ASQ-3) say "adjusted age". An adjusted age calculator and a corrected age calculator do the same sum.
What Is the Difference Between Corrected Age and Actual Age?
Corrected age counts from the due date, and actual (chronological) age counts from the birth date. The gap between the 2 ages always equals the weeks born early. A baby born at 32 weeks stays 8 weeks (56 days) younger by corrected age. That gap is 62% of the baby's life at 3 months, 15% at 12 months and 8% at 24 months, so it matters less every month.
How Do You Calculate Corrected Age for a 32-Week Baby?
To calculate corrected age for a 32-week baby, subtract 8 weeks (56 days) from the chronological age. 40 − 32 = 8 weeks early. A baby born at 32 weeks on 1 June 2026 has a due date of 27 July 2026. On 30 October 2026, the chronological age is 0;4;29 and the corrected age is 0;3;3.
Can Corrected Age Be Negative?
Yes, the corrected age formula gives a negative number until the baby reaches the due date. Neonatal teams use postmenstrual age for that period, so the calculator shows the time left until the due date instead of a negative figure. A baby born at 28 weeks on 1 October 2026 is due on 24 December 2026. On 30 October 2026, the baby is 7 weeks 6 days before the due date (a corrected age of −7 weeks 6 days) at a postmenstrual age of 32 weeks 1 day.
Should I Use Corrected Age for Developmental Milestones?
Yes, use corrected age for developmental milestones until about 2 years old. HealthyChildren.org says corrected age gives a better idea of when to expect milestones during the first 2 years. A baby born 8 weeks early who is 6 months old by the calendar is checked against 4-month milestones from the Centers for Disease Control and Prevention (CDC), such as holding the head steady without support and pushing up onto the forearms during tummy time. ASQ-3 adjusts for prematurity when a child was born 3 or more weeks early and is under 24 months old.
How Long Do You Correct Age for Prematurity?
You correct age for prematurity until 24 months (2 years). Clinics use 2 cut-offs: 24 months of chronological age (HealthyChildren.org and ASQ-3) or 24 months of corrected age (Starship Child Health, New Zealand). Starship notes that some authorities continue correction into childhood for cognitive function. Ask your pediatrician which cut-off your clinic follows.
Do You Use Corrected Age for Feeding and Growth?
Yes, use corrected age for feeding and growth in the first 2 years. Growth charts plot weight, length and head circumference at corrected age once the baby passes the due date. Before that, NICU teams plot growth on the Fenton preterm growth chart, which runs from 22 to 50 weeks of postmenstrual age. Solid foods start by corrected age plus 3 readiness signs: steady head control, sitting with support and opening the mouth for a spoon.
Is Corrected Age Used for Vaccinations?
No, corrected age is not used for vaccinations. The CDC vaccinates medically stable preterm babies at the same chronological age and with the same doses as full-term babies, so a baby born 10 weeks early gets the 2-month vaccines 2 months after birth. The 1 exception is the hepatitis B birth dose: a baby under 2,000 g (4.4 lb) whose mother tests negative for hepatitis B gets the first dose at 1 month of chronological age or at hospital discharge, whichever comes first.
Find your baby's corrected age
Enter the birth date, gestational age or due date and the check-up date. The corrected age calculator shows the corrected age, chronological age and postmenstrual age in one place.
Calculate corrected age