Corrected age for a baby born 15 weeks early (25 weeks)
A baby born 15 weeks early (at 25 weeks) has a corrected age fifteen weeks, about 3.4 months, below the calendar age. The AAP advises comparing development by corrected age for the first 2 years, so the 12-month CDC checklist applies from about 15.4 months, twelve months and fifteen weeks after birth.
Updated
Corrected age for a baby born 15 weeks early
Weeks early = 40 minus the weeks of pregnancy at birth. Everything is calculated in this browser; nothing is sent or saved.
Example: a child born April 15, 2025, checked on October 15, 2026 (18 months old). Enter your child's birth date.
- Corrected age
- 14 months 16 days
- about 14½ months, counted from the due date, July 29, 2025
- Chronological age
- 18 months
- about 18 months, counted from the birth date
- Stop correcting on
- April 15, 2027
- the second birthday (24 months chronological)
Born 15 weeks early means born at about 25 weeks of pregnancy, so the corrected age runs 15 weeks (about 3½ months) behind the age since birth. Until April 15, 2027, compare skills with the corrected age: between two checklist ages CDC says to use the earlier one, which is the 12-month checklist here. See what is emerging at 14 months.
When each CDC checklist applies for this child
Born 15 weeks early at a glance
| Born at | 25 weeks of pregnancy |
|---|---|
| Weeks early | 15 weeks = 105 days ≈ 3.4 months |
| 12-month checklist | from 15.4 months after birth |
| Correction stops | 24 months (corrected then: 20 mo 2 wk) |
Corrected age by month, born 15 weeks early
Age since birth minus fifteen weeks, in 30.4-day months; a dash means an earlier CDC checklist. The checklist changes in month sixteen, nineteen and twenty-two, then at twenty-four.
| Age since birth (months) | Corrected age (mo, wk) | CDC checklist (months) |
|---|---|---|
| 1 | due in 11 wk | – |
| 2 | due in 6 wk | – |
| 3 | due in 2 wk | – |
| 4 | 2 wk | – |
| 5 | 7 wk | – |
| 6 | 11 wk | – |
| 7 | 3 mo 2 wk | – |
| 8 | 4 mo 2 wk | – |
| 9 | 5 mo 2 wk | – |
| 10 | 6 mo 2 wk | – |
| 11 | 7 mo 2 wk | – |
| 12 | 8 mo 2 wk | – |
| 13 | 9 mo 2 wk | – |
| 14 | 10 mo 2 wk | – |
| 15 | 11 mo 2 wk | – |
| 16 | 12 mo 2 wk | 12 |
| 17 | 13 mo 2 wk | 12 |
| 18 | 14 mo 2 wk | 12 |
| 19 | 15 mo 2 wk | 15 |
| 20 | 16 mo 2 wk | 15 |
| 21 | 17 mo 2 wk | 15 |
| 22 | 18 mo 2 wk | 18 |
| 23 | 19 mo 2 wk | 18 |
| 24 | stop correcting | 24 |
When each CDC checklist applies, born 15 weeks early
Each corrected-age checklist starts fifteen weeks after its plain age; from the second birthday, calendar age. Dates: the example baby below (born 14 May 2025, due 27 August 2025).
| CDC checklist | Compare from (age since birth) | Example baby: in use |
|---|---|---|
| 12-month | 12 months + 15 weeks (about 15.4 months) | 27 August 2026 to 26 November 2026 |
| 15-month | 15 months + 15 weeks (about 18.4 months) | 27 November 2026 to 26 February 2027 |
| 18-month | 18 months + 15 weeks (about 21.4 months) | 27 February 2027 to 13 May 2027 |
| 24-month | 24 months: correction stops | 14 May 2027 to 13 November 2027 |
| 30-month | 30 months (calendar age) | 14 November 2027 to 13 May 2028 |
| 36-month | 36 months (calendar age) | from 14 May 2028 |
Worked example: a baby born 15 weeks early
A made-up baby, born on 14 May 2025, fifteen weeks early, with exact calendar dates.
-
Find the due date
14 May 2025 plus fifteen weeks (105 days) is 27 August 2025.
-
Age since birth
On 14 November 2026 the baby is exactly eighteen months old by the calendar.
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Corrected age
From 27 August 2025 to 14 November 2026 is fourteen months and eighteen days: the corrected age.
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Pick the checklist
Fourteen months and eighteen days is between 12 and 15 months: use the 12-month CDC checklist (the earlier one, as CDC advises) until the 15-month checklist on 27 November 2026.
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Stop correcting
14 May 2027 is the second birthday (corrected: twenty months and seventeen days); from then on, calendar age only.
Before the due date: the first three months
For the first fifteen weeks after birth the baby has not reached the due date, so the corrected age is below zero ("due in" in the table) for the first three monthly rows. Corrected-age milestones start to mean something once the due date has passed.
The fifteen-week gap matters most early on: at six months it is fifty-seven percent of the baby's age, at twelve months twenty-nine percent, and at twenty-three months only fifteen percent. Hence correction for the first two years only.
Corrected age at the AAP screening visits, 15 weeks early
The AAP recommends developmental screening at 9, 18 and 30 months and autism screening at 18 and 24 months. Ask your pediatrician which age they use; by corrected age:
- 9 months (14 February 2026 for the example baby): about five months and two weeks corrected, so an earlier CDC checklist (before 12 months).
- 18 months (14 November 2026): about fourteen months and two weeks corrected, matching the 12-month checklist.
- 24 months (14 May 2027): correction stops, so the 24-month checklist by calendar age.
- 30 months (14 November 2027): no correction; the 30-month checklist.
When to stop correcting for 15 weeks early
The AAP advises corrected age for the first 2 years, so for a baby born fifteen weeks early correction stops at 24 months chronological, when the corrected age is about twenty months and two weeks; the comparison then jumps to the 24-month checklist.
So the 18-month list is used for about 2.6 months (from eighteen months and fifteen weeks to the second birthday), not six.
Corrected age and real concerns
Being born fifteen weeks early is a reason to compare by corrected age, never a reason to wait on a worry: talk to your pediatrician if your baby loses a skill, misses milestones for their corrected age (at eighteen months by the calendar that means the 12-month checklist) or anything else concerns you. Many babies born early catch up by about age 2 (AAP). In the U.S. you can contact your state's Early Intervention program for children under 3 yourself; no doctor's referral is needed.
Frequently asked questions
How do you calculate corrected age for a baby born 15 weeks early?
Subtract fifteen weeks (or count from the due date). At six months: about eleven weeks corrected; at twelve months: eight months and two weeks; at eighteen: fourteen months and two weeks.
When does a baby born 15 weeks early reach the 12-month milestones?
From twelve months and fifteen weeks after birth (about 15.4 months); then the 15-month checklist at about 18.4 months and the 18-month one at about 21.4 months.
When do you stop using corrected age for 15 weeks early?
At 24 months chronological (AAP: first two years). On the second birthday the corrected age is about twenty months and two weeks; from then on, calendar age and the 24-month checklist.
What is 15 weeks early in weeks of pregnancy?
A baby born fifteen weeks before a forty-week due date is born at twenty-five weeks of pregnancy. The gap of 105 days, about 3.4 months, is what corrected age subtracts.
Related
Milestones by corrected age
Neighbouring weeks
Corrected age tools
By corrected age
Monitoring, not medical advice. Talk to your pediatrician about any concern. Our sources and method.