How to use the corrected age calculator
- Enter your baby's date of birth.
- Enter how many weeks pregnant you were at the birth, with any extra days (32 weeks and 4 days is written 32+4). If you know the due date instead, choose The due date and enter it.
- Check the Age on date. It starts as today; change it to see the corrected age at a check-up or on a birthday.
The result shows the corrected age in weeks and days, and in months counted from the due date, next to the age from birth. Copy result gives you the figures as text to take to an appointment.
Corrected age meaning (adjusted age)
A premature baby has two ages. The age from birth, also called the chronological age, counts from the day the baby was born. The corrected age, also called the adjusted age, counts from the date the baby was due, as if they had been born at full term. It is used because a baby born early has had less time to develop by any given date. An NHS trust's neonatal therapy team puts it simply:
"Motor development is measured from your baby's corrected age, that is from the date they were due"University Hospitals Dorset NHS Foundation Trust, Neonatal therapy service
How corrected age is worked out
HealthyChildren.org, the American Academy of Pediatrics' website for parents, gives the method: begin with your baby's actual age in weeks, then "subtract the number of weeks your baby was preterm." To find the weeks preterm, "subtract gestational age at birth from 40."
Weeks early = 40 weeks minus gestational age at birth
Corrected age = age from birth minus weeks early
HealthyChildren's own example is a baby born at 32 weeks, so 8 weeks early. At 16 weeks since birth, "her corrected age is 2 months", and she would be expected to have the skills of a 2-month-old baby born at term. With real dates:
| Born June 1, 2026 at 32 weeks | On September 21, 2026 |
|---|---|
| Age from birth | 16 weeks (3 months, 20 days) |
| Weeks early: 40 minus 32 | 8 weeks |
| Due date: June 1 plus 8 weeks | July 27, 2026 |
| Corrected age: 16 minus 8 | 8 weeks (1 month, 25 days) |
Weeks are exact; months are not, because months have different lengths. The calculator counts corrected age in months as a calendar age from the due date, so 8 weeks shows as 1 month and 25 days rather than a rounded 2 months. Extra days count too: a baby born at 32+4 was 7 weeks and 3 days early.
Before the due date: a negative corrected age
Until the due date arrives, the corrected age is below zero, so the calculator says how long is left instead. A baby born at 26+3 on September 1, 2026 was 13 weeks and 4 days early, so the due date is December 5, 2026. On October 8, 2026 the baby is 5 weeks and 2 days old from birth, and 8 weeks and 2 days before the due date. The corrected age is 0 on the due date and counts up from there.
When corrected age is used, and for how long
Corrected age is mainly used to judge development, such as when to expect a baby to smile, hold their head up or roll over. The CDC's "Learn the Signs. Act Early." milestone checklists say:
"If your child was born more than 3 weeks prematurely, use his/her corrected age."CDC, Learn the Signs. Act Early. online milestone checklists
So a baby born at 37 weeks or later (3 weeks early or less) needs no correction, and the calculator says so. That matches the CDC's definition of preterm birth: "before 37 weeks of pregnancy have been completed."
On how long, HealthyChildren.org says: "During the first 2 years, using your baby's corrected age will give you a better idea when he or she should reach common developmental goals." University Hospitals Dorset's neonatal team says they "generally make this correction for age until children are 2 years corrected age". After about age 2, ask your baby's doctor or health visitor whether to keep using it. Some things, such as vaccinations and feeding, may follow a different age, so ask which one applies.
Corrected age vs gestational age and age from birth
| Term | What it counts | Example: born at 32 weeks, 16 weeks ago |
|---|---|---|
| Gestational age at birth | Weeks of pregnancy when the baby was born | 32 weeks |
| Age from birth (chronological age) | Time since the birth date | 16 weeks |
| Corrected (adjusted) age | Time since the due date | 8 weeks |
Gestational age describes the pregnancy and stays fixed once the baby is born. Corrected age describes the baby afterwards and grows week by week, the same as the age from birth but 8 weeks behind in this example.
A guide, not a check-up
This preemie age calculator only does the date arithmetic. It cannot tell you whether a baby is developing well, and every baby is different. HealthyChildren.org reminds readers that its information "should not be used as a substitute for the medical care and advice of your pediatrician." If you have any concerns about your baby's growth or development, talk to your baby's doctor or health visitor.
Questions and answers
Is adjusted age the same as corrected age?
Yes. Both mean the baby's age counted from the due date instead of the birth date.
Does my baby need a corrected age if born at 37 weeks?
No. The CDC's milestone checklists use corrected age only for babies born more than 3 weeks early, so a baby born at 37 weeks or later uses the age from birth.
How long do you use corrected age for premature babies?
HealthyChildren.org says it helps during the first 2 years, and one NHS trust's neonatal team corrects until 2 years corrected age. Ask your baby's doctor or health visitor what applies to your baby.
Can corrected age be negative?
Yes, before the due date. The calculator shows it as weeks and days before the due date, and the corrected age starts at 0 on the due date.
What if I only know the due date?
Choose The due date and enter it. The weeks early are the days from the birth to the due date, and the gestation at birth is 40 weeks minus that.
Why does the corrected age in months not match 16 minus 8 weeks exactly?
Months are not all the same length, so the calculator counts months as calendar months from the due date. The weeks figure is the exact one.
Sources
Checked on 8 October 2026. If a rule has changed, please tell us.
- HealthyChildren.org (American Academy of Pediatrics): Corrected age for preemies
- CDC, Learn the Signs. Act Early.: 15 month online milestone checklist (corrected age)
- CDC, Learn the Signs. Act Early.: Milestone Tracker app
- CDC: Preterm birth
- University Hospitals Dorset NHS Foundation Trust: Neonatal therapy service