Why corrected age exists
A baby born at 28 weeks — the start of the WHO's very preterm category has spent twelve fewer weeks growing inside than a baby born at term. Those twelve weeks do not disappear at birth — the brain finishes them outside. So when we judge whether a preterm baby is developing as expected, we compare them against where they would be if they had been born on their due date. That adjusted number is the corrected age (also called adjusted age).
The arithmetic is simple, but it has to be redone at every single encounter, and every downstream judgement depends on it: which milestone list applies, which growth chart to plot on, which percentile, and when to stop correcting. Most tools do the date maths and stop there.
Corrected age, adjusted age and chronological age — what is the difference?
Corrected age and adjusted age are the same thing. Some clinics prefer one term, some the other, but both mean the baby's age counted from the original due date rather than the birthday. Chronological age is the plain time since birth. This site shows both because they are used for different decisions.
- Corrected or adjusted age: usually the right age for milestones and many preterm growth follow-up discussions.
- Chronological age: the right age for vaccines, many administrative forms and everyday birthday counting.
- Postmenstrual age (PMA): gestational age at birth plus days since birth; especially useful before the baby reaches term-equivalent age.
If you searched for an adjusted age calculator, you are in the right place — this tool calculates the same number.
What this tool does differently
- One input set, every answer. Corrected age, chronological age and postmenstrual age from the same two facts.
- Milestones are re-indexed automatically. The CDC/AAP surveillance prompts shown are the ones for the corrected age, not the birthday age.
- It remembers. Visits at 4, 8, 12, 18, 24 and 36 months corrected are kept as a serial record you can print or export.
- It never scores your baby. No pass, no fail, no reassuring verdict. The “act early” concerns are always visible.
- Your data stays on your device. No account, no server, no upload.
That makes the calculator the centre of a follow-up cluster: use the NICU follow-up schedule for visit timing, the late preterm baby guide for 34- to 36-week babies, and the solids guide when feeding questions start after discharge.
Corrected age is not used for everything
Two things in particular are not corrected: immunisations are given by chronological age, as the CDC immunization schedule by age is written, and the growth chart choice changes at term-equivalent age — preterm growth references such as Fenton's chart are used while the baby is still small. The tool shows the chronological number alongside the corrected one for exactly this reason.
Common corrected-age questions
What is corrected age for a premature baby?
Corrected age is chronological age minus the weeks of prematurity. Calculate prematurity from 40 weeks, then use the corrected number when reading early developmental milestones.
Is adjusted age the same as corrected age?
Yes. Adjusted age and corrected age are two names for the same number. Some parents search for one phrase and some for the other, but the calculation is identical.
What is PMA?
PMA means postmenstrual age. It is gestational age at birth plus the time since birth, and it is especially useful before the due date and in early neonatal follow-up. Use the PMA calculator when that is the number you need.
Should vaccines use corrected age?
No. Immunisations are scheduled by chronological age. Use the calculator’s chronological age for vaccine timing and corrected age for development-related conversations.
Should premature baby growth charts use corrected age?
In preterm follow-up, clinicians usually interpret early measurements against corrected age while also deciding which chart should be used at that stage. That is one reason the tool always shows corrected age and postmenstrual age side by side. Read the methodology for the growth-chart hand-off details.
My baby was born at 36 weeks. Do I still need corrected age?
Often yes, especially in the first year. For a four-month-old, even a two- to four-week difference changes which milestone row you should be reading. See the late preterm baby guide and the worked examples page.
When does corrected age stop being used?
Developmental correction is commonly used until about 24 months, although the appropriate endpoint can vary by developmental domain. Read when correction should stop and discuss your child’s follow-up plan with their clinician.
Continue with the preterm follow-up guides
Check the corrected-age formula, read the premature baby milestone chart, review the red flags that need medical attention, compare the terms on the adjusted age calculator page, use the PMA calculator, explore the preemie weight gain calculator, read the late preterm baby guide, check the NICU follow-up schedule, see when a preemie may be ready for solids, compare adjusted age vs chronological age, and use the preemie vaccines guide for one of the most common age mix-ups.