Corrected Age for Premature Babies

Born early? Then your baby has two ages. Here's what corrected age means, how to work it out, and when to use it - and when not to.

What is corrected age?

A pregnancy is full term at 40 weeks. A baby born before 37 weeks is premature - a "preemie".

A preemie has two ages:

• Real age - the time since the day your baby was born. Doctors call it chronological age.
• Corrected age - the real age minus the weeks your baby was born early. It's also called adjusted age.

Those early weeks were meant for growing inside the womb. Corrected age gives your baby that time back, so you compare them with babies at the same stage of growing up.

How to work out corrected age

There are two easy ways. Both give the same answer.

Count the weeks early

First, find how many weeks early your baby came: 40 minus the week of pregnancy they were born in. A baby born at 32 weeks came 8 weeks early. Then take your baby's real age and subtract those weeks.

Count from the due date

Corrected age is simply the time since your due date. Once your baby is past their due date, you can enter the due date in our calculator and the age it shows is the corrected age, in months, weeks, and days. Zodiac signs and birthstones go by the real birthday, so use the real birthday for those.

Before the due date

If your baby hasn't reached their due date yet, there is no corrected age to count. A baby born 8 weeks early who is 6 weeks old is still 2 weeks before term. In the hospital, doctors often count this time in weeks of pregnancy instead - for example, "38 weeks".

An example

Say your baby was born at 32 weeks and is now 5 months old:

• Real age: 5 months
• Weeks early: 40 - 32 = 8 weeks, which is about 2 months
• Corrected age: about 3 months

So for milestones, it's fair to compare your 5-month-old with a 3-month-old, not with other 5-month-olds. Want to turn weeks into months? See every week in months.

When to use corrected age

• Milestones. Smiling, rolling, sitting, and first words all follow corrected age. When you read our milestone guides, start with the one for your baby's corrected age. A 6-month-old born 8 weeks early fits the 4 months guide best.
• Growth and development checks. The American Academy of Pediatrics (AAP) says corrected age gives a better idea of when your baby should reach common goals.
• Until about age 2. The AAP advises using corrected age during the first 2 years. After that, the gap matters less and most families just use the real age. Your doctor may keep using it a little longer for a baby born very early.

When not to use it: shots

Vaccines follow the real birth date. US vaccine guidance (from the CDC's Advisory Committee on Immunization Practices) says preemies get their shots at the same real age, on the same schedule, as babies born on time. So the 2-month shots come 2 months after birth - even for a baby born 8 weeks early, whose corrected age is then zero.

The one exception is the first hepatitis B shot, which may be timed differently for very small babies. Your baby's care team will handle that.

Birthdays and special days count from the real birth date too. Your baby's 100 days and first birthday come 100 days and one year after the day they were born.

Sources

Corrected age, the example, and the "first 2 years" advice follow the American Academy of Pediatrics' guide Corrected Age For Preemies on HealthyChildren.org. The vaccine timing follows the CDC Advisory Committee on Immunization Practices' general best practice guidelines for preterm babies.

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