Adjusted Age Calculator (Premature Baby)
Calculate a premature baby’s adjusted (corrected) age from the birth date and due date. Example: a baby born on June 1, 2026 with a due date of July 20, 2026 is 7 weeks early; on September 15 the chronological age is 3 months 14 days and the adjusted age is 1 month 26 days.
Show steps
How to use the Adjusted Age Calculator (Premature Baby)
- Enter the values in the fields.
- Press Calculate to see the result with the steps shown.
Formula and method
Adjusted age = chronological age – (due date – birth date). Equivalent to counting age from the original due date instead of the birth date.
When to use adjusted age
| Use adjusted age for | Use chronological age for |
|---|---|
| Development and milestones | Vaccines |
| Growth charts | School entry dates |
| Starting solid foods (with your pediatrician) | Birthdays |
How far early is premature
| Born at | Called |
|---|---|
| 34 to 36 weeks | Late preterm |
| 32 to 33 weeks | Moderately preterm |
| 28 to 31 weeks | Very preterm |
| Before 28 weeks | Extremely preterm |
Examples of adjusted age
| Weeks early | Chronological age | Adjusted age |
|---|---|---|
| 4 | 6 months | 5 months 4 weeks |
| 8 | 6 months | 4 months |
| 12 | 12 months | 9 months |
| 16 | 12 months | 8 months |
Milestones and patience
Many preterm babies catch up on milestones by about 2 years. Talk to the pediatrician about any concern. This calculator is for education and is not medical advice. Your own doctor, midwife or pediatrician should guide decisions about your care.
Frequently asked questions
What is adjusted age?
Age counted from the due date for a premature baby.
How long do I use adjusted age?
Until about 2 years.
Do I use it for vaccines?
No, vaccines follow actual birth date.
How do I calculate it?
Subtract weeks born early from the actual age.
Does it apply to babies born at 37 weeks?
No, only to babies born before 37 weeks.
What if my baby is behind on milestones?
Ask your pediatrician about evaluation or early intervention.
Sources
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