Corrected age for a baby born 10 weeks early (30 weeks)
A baby born 10 weeks early (at 30 weeks) has a corrected age ten weeks, about 2.3 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 14.3 months, twelve months and ten weeks after birth.
Updated
Corrected age for a baby born 10 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
- 15 months 21 days
- about 15½ months, counted from the due date, June 24, 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 10 weeks early means born at about 30 weeks of pregnancy, so the corrected age runs 10 weeks (about 2½ 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.
When each CDC checklist applies for this child
Born 10 weeks early at a glance
| Born at | 30 weeks of pregnancy |
|---|---|
| Weeks early | 10 weeks = 70 days ≈ 2.3 months |
| 12-month checklist | from 14.3 months after birth |
| Correction stops | 24 months (corrected then: 21 mo 3 wk) |
Corrected age by month, born 10 weeks early
Age since birth minus ten weeks, in 30.4-day months; a dash means an earlier CDC checklist. The checklist changes in month fifteen, eighteen and twenty-one, then at twenty-four.
| Age since birth (months) | Corrected age (mo, wk) | CDC checklist (months) |
|---|---|---|
| 1 | due in 6 wk | – |
| 2 | due in 1 wk | – |
| 3 | 3 wk | – |
| 4 | 7 wk | – |
| 5 | 12 wk | – |
| 6 | 3 mo 3 wk | – |
| 7 | 4 mo 3 wk | – |
| 8 | 5 mo 3 wk | – |
| 9 | 6 mo 3 wk | – |
| 10 | 7 mo 3 wk | – |
| 11 | 8 mo 3 wk | – |
| 12 | 9 mo 3 wk | – |
| 13 | 10 mo 3 wk | – |
| 14 | 11 mo 3 wk | – |
| 15 | 12 mo 3 wk | 12 |
| 16 | 13 mo 3 wk | 12 |
| 17 | 14 mo 3 wk | 12 |
| 18 | 15 mo 3 wk | 15 |
| 19 | 16 mo 3 wk | 15 |
| 20 | 17 mo 3 wk | 15 |
| 21 | 18 mo 3 wk | 18 |
| 22 | 19 mo 3 wk | 18 |
| 23 | 20 mo 3 wk | 18 |
| 24 | stop correcting | 24 |
When each CDC checklist applies, born 10 weeks early
Each corrected-age checklist starts ten weeks after its plain age; from the second birthday, calendar age. Dates: the example baby below (born 21 October 2024, due 30 December 2024).
| CDC checklist | Compare from (age since birth) | Example baby: in use |
|---|---|---|
| 12-month | 12 months + 10 weeks (about 14.3 months) | 30 December 2025 to 29 March 2026 |
| 15-month | 15 months + 10 weeks (about 17.3 months) | 30 March 2026 to 29 June 2026 |
| 18-month | 18 months + 10 weeks (about 20.3 months) | 30 June 2026 to 20 October 2026 |
| 24-month | 24 months: correction stops | 21 October 2026 to 20 April 2027 |
| 30-month | 30 months (calendar age) | 21 April 2027 to 20 October 2027 |
| 36-month | 36 months (calendar age) | from 21 October 2027 |
Worked example: a baby born 10 weeks early
A made-up baby, born on 21 October 2024, ten weeks early, with exact calendar dates.
-
Find the due date
21 October 2024 plus ten weeks (seventy days) is 30 December 2024.
-
Age since birth
On 21 April 2026 the baby is exactly eighteen months old by the calendar.
-
Corrected age
From 30 December 2024 to 21 April 2026 is fifteen months and twenty-two days: the corrected age.
-
Pick the checklist
Fifteen months and twenty-two days is between 15 and 18 months: use the 15-month CDC checklist (the earlier one, as CDC advises) until the 18-month checklist on 30 June 2026.
-
Stop correcting
21 October 2026 is the second birthday (corrected: twenty-one months and twenty-one days); from then on, calendar age only.
Before the due date: the first two months
For the first ten 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 two monthly rows. Corrected-age milestones start to mean something once the due date has passed.
The ten-week gap matters most early on: at six months it is thirty-eight percent of the baby's age, at twelve months nineteen percent, and at twenty-three months only ten percent. Hence correction for the first two years only.
Corrected age at the AAP screening visits, 10 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 (21 July 2025 for the example baby): about six months and three weeks corrected, so an earlier CDC checklist (before 12 months).
- 18 months (21 April 2026): about fifteen months and three weeks corrected, matching the 15-month checklist.
- 24 months (21 October 2026): correction stops, so the 24-month checklist by calendar age.
- 30 months (21 April 2027): no correction; the 30-month checklist.
When to stop correcting for 10 weeks early
The AAP advises corrected age for the first 2 years, so for a baby born ten weeks early correction stops at 24 months chronological, when the corrected age is about twenty-one months and three weeks; the comparison then jumps to the 24-month checklist.
So the 18-month list is used for about 3.7 months (from eighteen months and ten weeks to the second birthday), not six.
Corrected age and real concerns
Being born ten 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 10 weeks early?
Subtract ten weeks (or count from the due date). At six months: about three months and three weeks corrected; at twelve months: nine months and three weeks; at eighteen: fifteen months and three weeks.
When does a baby born 10 weeks early reach the 12-month milestones?
From twelve months and ten weeks after birth (about 14.3 months); then the 15-month checklist at about 17.3 months and the 18-month one at about 20.3 months.
When do you stop using corrected age for 10 weeks early?
At 24 months chronological (AAP: first two years). On the second birthday the corrected age is about twenty-one months and three weeks; from then on, calendar age and the 24-month checklist.
What is 10 weeks early in weeks of pregnancy?
A baby born ten weeks before a forty-week due date is born at thirty weeks of pregnancy. The gap of seventy days, about 2.3 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.