Corrected Age Calculator
Work out a premature baby’s corrected (adjusted) age from the birth date and the weeks of pregnancy at birth, in weeks and months, with the dates the baby reaches each corrected-age milestone.
How to Use
- Enter the baby’s date of birth.
- Enter how many weeks and days pregnant the birth was (for example 32 weeks 0 days). It is on the discharge papers as the gestational age at birth.
- The On date starts at today; change it to see the corrected age on any other day, such as a check-up.
- Read the corrected age, the actual age and how early the baby was born. Under 6 months the corrected age is shown in weeks first; after that in months.
- The table lists the dates the baby reaches a corrected age of 2, 4, 6, 9, 12, 18 and 24 months, with the actual age on each date.
Worked Example
Born at 32 weeks. A baby was born on Friday 1 May 2026 at 32 weeks 0 days, so 40 − 32 = 8 weeks early, and the due date was Friday 26 June 2026. On Friday 21 August 2026 the baby is 112 days old, 16 weeks 0 days. The corrected age is 16 − 8 = 8 weeks 0 days: the time since the due date, which by the calendar is 1 month 26 days. This is the example HealthyChildren.org gives: a 4-month-old with the skills expected of a 2-month-old is on track.
The common mistake: counting from 37 or 39 weeks. Term starts at 37 weeks and full term at 39, but the correction is counted from 40 weeks, the due date. Taking 37 − 32 = 5 weeks would give a corrected age of 11 weeks instead of 8, and the baby would be compared with milestones three weeks too old.
Before the due date. A baby born at 30 weeks 0 days on 1 September 2026 is 33 days old on 4 October 2026 and has no corrected age yet: the due date, 10 November, is 37 days away. The postmenstrual age is 30w 0d + 4w 5d = 34 weeks 5 days.
Show Work
Formulas
Why Babies Born Early Get a Second Age
A baby born 8 weeks early has had 8 fewer weeks in the womb, so at the same birthday is not expected to do what a baby born on time does. Counting from the due date puts both on the same footing. HealthyChildren.org, the parent site of the American Academy of Pediatrics, explains the method in “Corrected Age For Preemies”, adapted from the Academy’s book Understanding the NICU, and recommends it for the first 2 years.
The words matter too. In 2004 the Academy’s Committee on Fetus and Newborn published a policy statement, “Age Terminology During the Perinatal Period” (Engle, Pediatrics), asking for consistent use of gestational age, postmenstrual age, chronological age and corrected age, so that growth and development results from different hospitals and studies mean the same thing.
About This Calculator
This calculator works out a premature baby’s corrected age on any date from the birth date and the gestational age at birth, in weeks and in calendar months, alongside the actual age and how early the baby was born. Before the due date it gives the postmenstrual age instead. The table shows the dates of the corrected-age milestones up to 2 years. It counts whole calendar days, so time zones never shift the answer.
Dates stay in your browser; nothing is sent anywhere.
For general information only — not medical advice. Talk to a doctor or other qualified professional about your own health and your baby’s.
Related tools: Pregnancy Weight Gain Calculator, Ovulation Calculator, and hCG Doubling Time Calculator.
Frequently Asked Questions
What is corrected age?
The age a baby born early would be if born on the due date: actual age minus the weeks born early, where weeks early = 40 − gestational age at birth. HealthyChildren.org (American Academy of Pediatrics) gives the example of a baby born at 32 weeks, 8 weeks early: at 16 weeks old the corrected age is 16 − 8 = 8 weeks, about 2 months.
How long is corrected age used?
HealthyChildren.org advises using it during the first 2 years, when comparing development with what is expected for a baby’s age. For a baby born at 28 weeks 3 days on 10 December 2025, the due date was 1 March 2026, so a corrected age of 2 years is reached on 1 March 2028, when the baby is 2 years, 2 months and 20 days old.
What if the baby has not reached the due date yet?
Then there is no corrected age yet; age is often given as postmenstrual age, the weeks of pregnancy at birth plus the time since. A baby born at 30 weeks on 1 September 2026 is 33 days old on 4 October 2026, so 30w 0d + 4w 5d = 34w 5d, with the due date 37 days away on 10 November.
Is adjusted age the same as corrected age?
Yes, in everyday use both mean age counted from the due date instead of the birth date. The American Academy of Pediatrics’ 2004 policy statement on age terminology asked for standard terms (gestational age, postmenstrual age, chronological age and corrected age among them) so that results from different studies and clinics can be compared.
Does a baby born at 38 weeks need a corrected age?
Births from 37 weeks 0 days count as term (ACOG Committee Opinion 579), so the difference is small: a baby born at 38 weeks 2 days was 1 week 5 days before the due date, and at 16 weeks 4 days old has a corrected age of 14 weeks 6 days. Ask your baby’s doctor whether they correct for it.
How do I use the Corrected Age Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Milestone checks
A baby born at 32 weeks who is 4 months old (16 weeks) is compared with 2-month milestones, because the corrected age is 8 weeks.
Very early births
Born at 24 weeks 6 days on 20 March 2025, the baby was 15 weeks 1 day early; on 4 October 2026 the actual age is 1 year 6 months 14 days and the corrected age 1 year 3 months 0 days.
In the NICU
Born at 30 weeks on 1 September 2026, the baby is 34 weeks 5 days postmenstrual age on 4 October, with the due date on 10 November.
Planning check-ups
Born at 28 weeks 3 days on 10 December 2025, the corrected 9-month mark falls on 1 December 2026, when the baby is 11 months 21 days old.
Late preterm
Born at 35 weeks on 15 January 2025, 5 weeks early: on 4 October 2026 the corrected age is 1 year 7 months 15 days, against an actual age of 1 year 8 months 19 days.
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