Corrected Age Calculator for Premature Babies
This corrected age calculator works out how old a premature baby would be if they had been born on their due date. Enter the date of birth and either the due date or the gestational age at birth in weeks and days, and the tool returns the chronological age, the corrected age and the number of weeks the baby was born early. Parents and clinicians use the corrected figure to judge development fairly.
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Corrected age today
A baby born eight weeks early who is now six months old has a corrected age of about four months. Comparing that baby with full term six month olds would make normal progress look like a delay. Corrected age, also called adjusted age, removes that unfair comparison.
How to Use the Corrected Age Calculator
Type the baby’s date of birth first. Then enter the original due date, or the gestational age at birth, such as 31 weeks and 4 days, if you know that instead. Press Calculate and the corrected age calculator shows chronological age, corrected age and postmenstrual age side by side.
The corrected age calculator updates daily, so you can bookmark the page and check it before each appointment. If your baby was born at 37 weeks or later, the tool notes that no correction is needed. Babies born at term are not considered premature for this purpose.
Three steps
- 1Enter the birth dateThe day the baby was born.
- 2Add the due date or weeks at birthFor example 31 weeks and 4 days.
- 3Read three agesChronological, corrected and postmenstrual side by side.
How Corrected Age Is Calculated
Corrected age equals chronological age minus the number of weeks the baby arrived early. Weeks early is 40 minus the gestational age at birth, since 40 weeks is the standard length of a full term pregnancy. A baby born at 30 weeks is 10 weeks early, so at 26 weeks old the corrected age is 16 weeks.
The same answer comes from counting the time since the due date instead of the birth date. That shortcut is why parents who know the due date can use it directly in the calculator. The corrected age calculator shows the result in weeks for young babies and in months and weeks once the baby is older.
| Chronological age | 6 months |
| Weeks early | 40 minus 32 = 8 weeks |
| Corrected age | About 4 months |
Counting from the due date instead of the birth date gives the same answer.
When to Use Corrected Age
Corrected age is used for developmental milestones such as smiling, sitting, crawling and first words. Pediatricians also plot growth on charts using corrected age in the early months, which gives a clearer picture of catch up growth. Many feeding decisions, such as when to start solid foods, are also guided by corrected age and readiness signs.
Vaccinations are the main exception. Immunizations are scheduled by chronological age, so a preemie gets two month shots two months after birth regardless of corrected age. Mixing the two up can delay important protection, so always confirm the schedule with your pediatrician.
Smiling, sitting, crawling, first words and early growth charts.
Shots follow the time since birth, so two month shots come two months after birth.
When to Stop Correcting for Prematurity
Most clinicians use corrected age until about 2 years, by which point many premature children have caught up. Children born very early, before about 28 weeks, may be followed with corrected age for longer in some developmental assessments. Your care team will tell you when to switch to chronological age.
The difference matters less as a child grows, because a two month gap is large at six months but small at three years. Developmental tests used in early intervention often state in the manual whether to correct. The chronological age calculator on this site is the right tool once correction ends.
Typical timeline
- BirthChronological age starts counting
- Due dateCorrected age starts counting
- About 2 yearsMost clinicians stop correcting
Corrected Age vs Postmenstrual Age
Postmenstrual age is the gestational age at birth plus the time since birth, and neonatal units use it to track babies while they are still in the hospital. A baby born at 28 weeks who is now 6 weeks old has a postmenstrual age of 34 weeks. Once a baby passes 40 weeks postmenstrual age, corrected age takes over as the more useful measure.
Corrected gestational age is another name you may see for the same idea in the NICU. Hospitals in different countries use slightly different terms, which confuses many parents. The corrected age calculator shows both values so you can match whatever your hospital uses.
| Gestational age at birth | 28 weeks |
| Time since birth | 6 weeks |
| Postmenstrual age | 34 weeks |
NICU teams use postmenstrual age while the baby is still in hospital.
Frequently Asked Questions
How do I calculate my baby’s corrected age?
Subtract the number of weeks your baby was born early from their age since birth. Weeks early equals 40 minus the gestational age at birth. The result is the corrected age.
Until what age do you use corrected age?
Most doctors use corrected age until about 2 years old. Some very premature children are assessed with corrected age a little longer. Your pediatrician will advise on the right time to stop.
Are vaccines given by corrected age?
No, vaccines follow the chronological age from the actual birth date. A premature baby receives two month vaccines two months after birth. This keeps protection on schedule.
Is adjusted age the same as corrected age?
Yes, adjusted age and corrected age mean the same thing. Both subtract the weeks born early from the chronological age. Different hospitals and websites simply prefer different terms.
Does a baby born at 37 weeks need a corrected age?
No, babies born at 37 weeks or later are considered term. Their chronological age is used for milestones and growth. Correction applies only to babies born before 37 weeks.