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Adjusted & Corrected Age Calculator
Corrected age (also called adjusted age) is your premature baby's age calculated from their original due date — not their actual birthday. Pediatricians use it to evaluate development, growth, and milestones more accurately for preemies.
Fill both fields above to see your baby’s corrected age.
This tool is for general information only and isn’t medical advice. Always follow your pediatrician or neonatologist for guidance about your baby.
How to calculate corrected age by hand
There are two routes to the same number. Use whichever one you have in front of you — they always agree.
From your due date
Corrected age is just how long it has been since your original due date. If the due date was March 1 and today is September 1, your baby's corrected age is six months — whatever day they were actually born.
From gestational age at birth
Subtract the weeks of prematurity from your baby's chronological age: corrected age = chronological age − (40 weeks − gestational age at birth).
| Born at | Weeks early | Chronological age | Corrected age |
|---|---|---|---|
| 32 weeks | 8 weeks | 6 months | 4 months |
| 27 weeks | 13 weeks | 14 months | about 11 months |
| 35 weeks | 5 weeks | 3 months | about 7 weeks |
Forty weeks is the reference point because that is what a due date marks. Correction is conventionally applied to babies born before 37 weeks.
Corrected age chart by gestational age
The gap between the calendar and your baby's corrected age is set on the day they are born and never grows. Find the week they arrived, and read across to see what their corrected age will be at each of the usual checkpoints.
| Born at | Weeks early | At 6 mo old | At 12 mo old | At 18 mo old | At 24 mo old |
|---|---|---|---|---|---|
| 24 weeks | 16 | 2 mo | 8 mo | 14 mo | 20 mo |
| 26 weeks | 14 | 2.5 mo | 8.5 mo | 14.5 mo | 20.5 mo |
| 28 weeks | 12 | 3 mo | 9 mo | 15 mo | 21 mo |
| 30 weeks | 10 | 3.5 mo | 9.5 mo | 15.5 mo | 21.5 mo |
| 32 weeks | 8 | 4 mo | 10 mo | 16 mo | 22 mo |
| 34 weeks | 6 | 4.5 mo | 10.5 mo | 16.5 mo | 22.5 mo |
| 36 weeks | 4 | 5 mo | 11 mo | 17 mo | 23 mo |
Rounded using the clinical shorthand of four weeks to a month. The calculator above works from your real dates, so use it for anything you are writing down.
Chronological, corrected, and corrected gestational age
Three numbers get used for the same baby, sometimes in the same conversation. They are not interchangeable.
- Chronological age
- Time since birth — what the calendar says, and what you put on the birthday card. Vaccines and well-child visits run on this one.
- Corrected age (adjusted age)
- Time since the original due date. Milestones run on this one until 24 months chronological age, and your pediatrician may plot growth using it too. It is what the calculator above returns, and the two names mean exactly the same thing.
- Corrected gestational age (postmenstrual age, PMA)
- Gestational age at birth plus the weeks since — a baby born at 28 weeks who is 6 weeks old is 34 weeks PMA. Counted in weeks, and mostly used while you are still in the NICU. Past 40 weeks PMA the team stops using it and switches to corrected age. The NICU day counter tracks this one for you.
What corrected age is used for — and what it isn't
Use corrected age
- Developmental milestones — rolling, sitting, first words
- Growth charts — your pediatrician may plot weight, length and head circumference using corrected age
- Early intervention evaluations and eligibility
- Readiness for solids, and what to expect of sleep
Use chronological age
- Vaccines — the standard schedule runs from the birth date
- RSV protection — timed to the season and the birth date
- Well-child visit scheduling
- Car seat limits — set by weight and height, not by age at all
- Their birthday. Correcting is a clinical tool, not a second birthday
The vaccine one matters most. It is the single most common mix-up, and correcting the schedule would leave your baby unprotected for weeks at the age they are most vulnerable. More on why corrected age matters →
Adjusted age — common questions
How do I calculate my baby's adjusted age?
Take your baby’s chronological age (time since birth) and subtract the number of weeks or months they were born early. For example, a 6-month-old born 8 weeks early has an adjusted age of about 4 months. The calculator above does this for you from either your due date or gestational age at birth.
How long should I use adjusted age?
Most pediatricians use corrected age until around age 2, when the developmental gap from prematurity has typically closed. For babies born very early (before 28 weeks), some specialists continue correcting until age 3. Your own medical team’s guidance comes first.
Do vaccines follow adjusted or chronological age?
Chronological age. Premature babies receive vaccines on the standard schedule based on their actual birth date, not their corrected age, with rare exceptions decided by their medical team.
Is adjusted age used for growth charts?
In the NICU, many teams use a preterm growth chart such as the Fenton chart. After that, your pediatrician may plot your baby’s weight, length, and head circumference using corrected age. Practices differ, so it’s worth asking which age and which chart they’re using.
Are adjusted age and corrected age the same thing?
Yes — adjusted age and corrected age mean the same thing and are used interchangeably. Both describe your baby’s age counted from their original due date instead of their birth date.
Does this also work as a corrected age calculator?
Yes. Adjusted age and corrected age are the same measurement, so this is a corrected age calculator too. You can enter either your due date or your baby’s gestational age at birth, and it returns the corrected age your pediatrician uses to track a premature baby’s milestones (and often growth).
What is the difference between chronological age and adjusted age?
Chronological age counts from the day your baby was born. Adjusted age counts from their original due date. For a baby born 10 weeks early the two differ by 10 weeks, and that gap stays exactly the same for as long as correction is used — it never widens. Vaccines and appointment scheduling follow chronological age; milestones follow adjusted age, and your pediatrician may plot growth using corrected age too.
What is corrected gestational age?
Corrected gestational age — more precisely called postmenstrual age, or PMA — is your baby’s gestational age at birth plus the weeks since. A baby born at 28 weeks who is now 6 weeks old is 34 weeks PMA. It is counted in weeks rather than months and is mostly used while your baby is still in the NICU. Once they pass 40 weeks PMA, which is the original due date, teams switch over to corrected age in months.
Do you correct for a baby born at 35 or 36 weeks?
Correction is conventionally applied to babies born before 37 weeks, so a late preterm baby born at 34–36 weeks is usually corrected — often for the first year, since even a few weeks is visible at this stage. Babies born at 37 weeks or later aren’t preterm — 37–38 weeks is called early term and 39–40 full term — and are not corrected. Your pediatrician’s own practice is what counts.
Approaching the two-year mark? Read: When to stop adjusting age for preemies →
How we keep this accurate
Written by a preemie dad and grounded in CDC “Learn the Signs. Act Early.”, AAP, and March of Dimes guidance — checked against those sources. Use this as a conversation starter with your care team, not a substitute for it. Full disclaimer.