Corrected age for a baby born 6 weeks early (34 weeks)
A baby born 6 weeks early (at 34 weeks) has a corrected age six weeks, about 1.4 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 13.4 months, twelve months and six weeks after birth.
Updated
Corrected age for a baby born 6 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
- 16 months 18 days
- about 16½ months, counted from the due date, May 27, 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 6 weeks early means born at about 34 weeks of pregnancy, so the corrected age runs 6 weeks (about 1½ 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 15-month checklist here. See what is emerging at 16 months.
When each CDC checklist applies for this child
Born 6 weeks early at a glance
| Born at | 34 weeks of pregnancy |
|---|---|
| Weeks early | 6 weeks = 42 days ≈ 1.4 months |
| 12-month checklist | from 13.4 months after birth |
| Correction stops | 24 months (corrected then: 22 mo 3 wk) |
Corrected age by month, born 6 weeks early
Age since birth minus six weeks, in 30.4-day months; a dash means an earlier CDC checklist. The checklist changes in month fourteen, seventeen and twenty, then at twenty-four.
| Age since birth (months) | Corrected age (mo, wk) | CDC checklist (months) |
|---|---|---|
| 1 | due in 2 wk | – |
| 2 | 3 wk | – |
| 3 | 7 wk | – |
| 4 | 11 wk | – |
| 5 | 3 mo 3 wk | – |
| 6 | 4 mo 3 wk | – |
| 7 | 5 mo 3 wk | – |
| 8 | 6 mo 3 wk | – |
| 9 | 7 mo 3 wk | – |
| 10 | 8 mo 3 wk | – |
| 11 | 9 mo 3 wk | – |
| 12 | 10 mo 3 wk | – |
| 13 | 11 mo 3 wk | – |
| 14 | 12 mo 3 wk | 12 |
| 15 | 13 mo 3 wk | 12 |
| 16 | 14 mo 3 wk | 12 |
| 17 | 15 mo 3 wk | 15 |
| 18 | 16 mo 3 wk | 15 |
| 19 | 17 mo 3 wk | 15 |
| 20 | 18 mo 3 wk | 18 |
| 21 | 19 mo 3 wk | 18 |
| 22 | 20 mo 3 wk | 18 |
| 23 | 21 mo 3 wk | 18 |
| 24 | stop correcting | 24 |
When each CDC checklist applies, born 6 weeks early
Each corrected-age checklist starts six weeks after its plain age; from the second birthday, calendar age. Dates: the example baby below (born 10 May 2024, due 21 June 2024).
| CDC checklist | Compare from (age since birth) | Example baby: in use |
|---|---|---|
| 12-month | 12 months + 6 weeks (about 13.4 months) | 21 June 2025 to 20 September 2025 |
| 15-month | 15 months + 6 weeks (about 16.4 months) | 21 September 2025 to 20 December 2025 |
| 18-month | 18 months + 6 weeks (about 19.4 months) | 21 December 2025 to 9 May 2026 |
| 24-month | 24 months: correction stops | 10 May 2026 to 9 November 2026 |
| 30-month | 30 months (calendar age) | 10 November 2026 to 9 May 2027 |
| 36-month | 36 months (calendar age) | from 10 May 2027 |
Worked example: a baby born 6 weeks early
A made-up baby, born on 10 May 2024, six weeks early, with exact calendar dates.
-
Find the due date
10 May 2024 plus six weeks (forty-two days) is 21 June 2024.
-
Age since birth
On 10 August 2025 the baby is exactly fifteen months old by the calendar.
-
Corrected age
From 21 June 2024 to 10 August 2025 is thirteen months and twenty days: the corrected age.
-
Pick the checklist
Thirteen months and twenty 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 21 September 2025.
-
Stop correcting
10 May 2026 is the second birthday (corrected: twenty-two months and nineteen days); from then on, calendar age only.
The first months after a birth at 34 weeks
For the first six weeks after birth the baby has not reached the due date, so the one-month row shows the due date still ahead. From the second month on the corrected age is positive and climbs one month at a time.
The six-week gap matters most early on: at six months it is twenty-three percent of the baby's age, at twelve months eleven percent, and at twenty-three months only six percent. Hence correction for the first two years only.
Corrected age at the AAP screening visits, 6 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 (10 February 2025 for the example baby): about seven months and three weeks corrected, so an earlier CDC checklist (before 12 months).
- 18 months (10 November 2025): about sixteen months and three weeks corrected, matching the 15-month checklist.
- 24 months (10 May 2026): correction stops, so the 24-month checklist by calendar age.
- 30 months (10 November 2026): no correction; the 30-month checklist.
When to stop correcting for 6 weeks early
The AAP advises corrected age for the first 2 years, so for a baby born six weeks early correction stops at 24 months chronological, when the corrected age is about twenty-two months and three weeks; the comparison then jumps to the 24-month checklist.
So the 18-month list is used for about 4.6 months (from eighteen months and six weeks to the second birthday), not six.
Corrected age and real concerns
Being born six 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 15-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 6 weeks early?
Subtract six weeks (or count from the due date). At six months: about four months and three weeks corrected; at twelve months: ten months and three weeks; at eighteen: sixteen months and three weeks.
When does a baby born 6 weeks early reach the 12-month milestones?
From twelve months and six weeks after birth (about 13.4 months); then the 15-month checklist at about 16.4 months and the 18-month one at about 19.4 months.
When do you stop using corrected age for 6 weeks early?
At 24 months chronological (AAP: first two years). On the second birthday the corrected age is about twenty-two months and three weeks; from then on, calendar age and the 24-month checklist.
What is 6 weeks early in weeks of pregnancy?
A baby born six weeks before a forty-week due date is born at thirty-four weeks of pregnancy. The gap of forty-two days, about 1.4 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.