Calculated on your phone. The dates stay on it.
- Corrected age = actual age − how many weeks early your baby was born. Weeks early = 40 − the weeks of pregnancy at birth.
- Use it until about 2 years for growth charts and milestones, as the American Academy of Pediatrics advises.
- Born at 37 weeks or later? That's term: there's nothing to correct.
- Vaccines go by the actual age, never the corrected one.
How corrected age is calculated
Take your baby's actual age, counted from the birthday, and subtract the number of weeks they arrived early. To get the weeks early, subtract the weeks of pregnancy at birth from 40. A baby born at 32 weeks is 8 weeks (2 months) early, so at 4 months old their corrected age is 2 months. That is the age to compare them with: a 4-month-old born at 32 weeks is developmentally a 2-month-old, and right on track if they behave like one.
With the due date it's even simpler: corrected age is the time since the due date. That's why the due date gives the most exact answer; weeks and days of gestation work just as well if that's what the hospital wrote down.
| Born at | Weeks early | Actual age 6 months | Actual age 12 months |
|---|---|---|---|
| 36 weeks | 4 weeks | about 5 months | about 11 months |
| 32 weeks | 8 weeks | about 4 months | about 10 months |
| 28 weeks | 12 weeks | about 3 months | about 9 months |
| 24 weeks | 16 weeks | about 2 months | about 8 months |
Corrected age in the last two columns. Months here are rounded to whole months; the calculator above gives months and weeks.
What corrected age is for
- Growth charts. A premature baby's weight, length and head are plotted at their corrected age until about 2 years. The growth percentile calculator does this when you open "Born early?" and add the due date or the weeks.
- Milestones. Smiling, rolling, sitting and crawling are judged against the corrected age. A 6-month-old born 3 months early is doing well if they do what a 3-month-old does.
- What to expect day to day. Typical feeds, naps and wake windows fit the corrected age better than the birthday, especially in the first year.
- Not for vaccines. Premature babies get their vaccines at the same actual age and on the same schedule as babies born at term (CDC).
When to stop correcting
The American Academy of Pediatrics uses corrected age for the first 2 years. By then most premature babies have caught up, and the few weeks' difference no longer changes much, so from the second birthday pediatricians use the actual age. Babies born very early are sometimes followed with a corrected age a little longer; if your NICU follow-up team does that, go with them.
Before the due date
Until a premature baby reaches the due date, the corrected age is below zero, and the term-baby charts don't apply yet. In the NICU, doctors use preterm growth charts such as Fenton or INTERGROWTH-21st, and often talk about postmenstrual age: the weeks of pregnancy at birth plus the weeks since. A baby born at 30 weeks who is 6 weeks old is 36 weeks postmenstrual. From the due date on, the WHO charts take over with the corrected age.
Questions
Is corrected age the same as adjusted age?
Yes. Corrected age and adjusted age are two names for the same thing: the age counted from the due date instead of the birth date.
Is a baby born at 36 weeks premature?
Yes. Any baby born before 37 weeks is preterm; 34 to 36 weeks is called late preterm. The correction is small, 4 weeks at 36 weeks, and matters most in the first months, when 4 weeks is a big share of a baby's life.
Should I use corrected age for vaccines?
No. The CDC recommends vaccinating premature babies at the same actual (chronological) age and on the same schedule as babies born at term. Corrected age is for growth and development only.
Do I use corrected age for weight percentiles?
Yes, until about 2 years. Compare your baby with babies of the same corrected age: a 6-month-old born 8 weeks early belongs on the 4-month table, not the 6-month one. The growth calculator does this for you.
What if I only know the weeks, not the due date?
That works too. Pick the weeks and days of pregnancy at birth, as written in the discharge papers (for example 31 weeks and 4 days), and the calculator works out the due date from it.
Is what I type private?
Yes. It's calculated on your phone and saved only on your phone, the same way Mamoon keeps your nursery video on your own Wi-Fi.
Sources
- American Academy of Pediatrics, HealthyChildren.org, Corrected age for preemies (the formula and its use in the first 2 years).
- CDC, General best practices for immunization: special situations (preterm babies are vaccinated by chronological age).
- World Health Organization, Preterm birth fact sheet (born before 37 weeks).
- CDC, Recommended growth charts and the WHO Child Growth Standards.
Spotted a mistake or an outdated figure? Write to [email protected].