How to use the corrected age calculator for premature babies
- Enter the baby's date of birth, the weeks of pregnancy at birth and any extra days.
- Choose the date to measure age on. It starts as today.
- Open the advanced option if the care team counts from a full-term reference other than 40 weeks.
- Read the corrected age, the age since birth and the date full term would have been reached, plus the table of calendar dates for 1, 2, 3, 6, 9, 12, 18 and 24 months of corrected age.
Formula
days born early = full-term reference weeks x 7 - (weeks at birth x 7 + extra days)
full-term date = date of birth + days born early
corrected age = date measured - full-term date
age since birth = date measured - date of birth
The age in months and days counts whole calendar months from the starting date. If the full-term reference is reached or passed at birth, the two ages are the same.
Born at 32 weeks
A baby born on March 2, 2026 after 32 weeks of pregnancy was born 8 weeks (56 days) before the 40-week reference. Full term would have been reached on Monday, April 27, 2026. On October 2, 2026 the baby is 30 weeks and 4 days old since birth (7 months), and the corrected age is 22 weeks and 4 days (5 months, 5 days).
The date when the corrected age reaches 6 months is Tuesday, October 27, 2026, 3 weeks and 4 days after October 2. Before April 27 the page reports that the full-term date is still ahead. With 35 weeks and 3 days at birth, the baby was born 4 weeks and 4 days early.
What this page does
Corrected age is the age a baby would be if it had been born at full term. It is a way of counting time, found by taking away the weeks the baby was born early. This page does only that date arithmetic. It does not tell you what to expect at any age, how to judge feeding, growth, vaccines or development, or when to stop using a corrected age.
How long to use a corrected age, and what it means for your child, is a question for your child's doctor or nurse. Do not use this page to judge how a baby is doing. For plain date calculations, see the age calculator, the date calculator and the days between dates calculator.
Full-term references
The usual reference is 40 weeks, but some sources count from 37 or 38 weeks, so the reference is a setting you can change. The result moves by the same number of weeks. If the care team gives you a due date, you can also work from that: the full-term date shown here is the date to compare it with. Another date tool for animals and eggs is the egg incubation calendar calculator.
Assumptions and limits
- Weeks of pregnancy at birth are between 20 and 42 whole weeks, with 0 to 6 extra days.
- The full-term reference is between 36 and 42 weeks and is 40 by default.
- Dates are calendar dates, without time zones. Months are whole calendar months from the starting date.
- The page gives no medical interpretation of any age.
Frequently asked questions
Is corrected age the same as age since the due date?
If the due date was 40 weeks from the start of the pregnancy, yes. This page counts from the full-term date implied by the weeks at birth, which matches the due date when the dating is the same.
What if the baby was born at or after the full-term reference?
Then no weeks are subtracted and the two ages match. The page says so.
Why are there two ages in months?
One counts calendar months from the date of birth and the other from the full-term date. They differ by roughly the number of months the baby was born early.
Can I use it for older children?
The arithmetic works for any date after birth. How long a corrected age is used, if at all, is something to ask the child's doctor.