Corrected age calculator for preterm infants
Enter the gestational weeks at birth and the dates of birth and assessment. You get the corrected age in days, weeks and months, the preterm classification and the formula step by step.
For: Preterm infants: age is corrected up to 24 months for those born before 32 weeks and up to 12 months for the rest. Free, no sign-up. Everything is worked out in your browser and nothing is stored.
How corrected age is worked out
Corrected age subtracts from the chronological age the time the baby was short of being born at 40 weeks, the estimated due date:
Corrected age (days) = chronological age (days) − [(40 − gestational weeks) × 7]
The multiplication by 7 turns weeks into days. If the gestational age is over 40 weeks, 40 is used. Example: born at 32 weeks and now 90 days old. 90 − [(40 − 32) × 7] = 90 − 56 = 34 days, that is, 4 completed weeks of corrected age.
Classification and how long age is corrected
| Gestational weeks at birth | Classification | Age corrected up to |
|---|---|---|
| Under 32 | Extremely preterm | 24 months |
| 32 and 33 | Moderately preterm | 12 months |
| 34 to 36 | Late preterm | 12 months |
| 37 or more | Not classified as preterm | 12 months |
How to read the result
- Positive corrected age: it is shown in days, in completed weeks and in months and days, alongside the chronological age, for use in assessing growth and development.
- Past the limit: if the corrected age goes beyond 24 or 12 months depending on the group, the calculator reports that age is no longer corrected.
- Corrected age of 0 days or less: the baby has not yet reached 40 weeks; the result is given in weeks of corrected age (34 weeks, for instance).
Months are counted as in the rest of the NUTRYSoft calculators: completed years and months between the two dates, adding one month when more than 15 days are left over.
Frequently asked questions
What is corrected age?
It is the age a preterm baby would have if they had been born on the estimated due date, at 40 weeks. It is worked out by subtracting from the chronological age the weeks that were missing to reach 40.
How is corrected age calculated?
Corrected age in days = chronological age in days − (40 − gestational weeks at birth) × 7. For example, a baby born at 32 weeks who is 90 days old: 90 − (8 × 7) = 34 days of corrected age.
Up to what age is it corrected?
In this calculator, up to 24 months for babies born before 32 weeks (extremely preterm) and up to 12 months for those born at 32 weeks or later. Past that limit it reports that age is no longer corrected.
What if the baby has not yet reached 40 weeks?
If the corrected age comes out as 0 days or less, the result is given in weeks: 40 plus the corrected age divided by 7, rounded. For example, −44 days is 34 weeks of corrected age.
What if the baby was born after 40 weeks?
The calculation uses 40 weeks, so the corrected age is the same as the chronological age.
Is the data I enter stored?
No. Everything is worked out in your browser; no data is sent or stored.
Source
Norma Técnica para la supervisión de niños y niñas de 0 a 9 años en la Atención Primaria de Salud (Technical standard for the health supervision of children aged 0 to 9 in primary care). Ministerio de Salud, Chile, 2014.
A support tool for health professionals. It does not replace clinical assessment or the technical standard in force.