A Month and a Half or 10 Days Old? Calculating Adjusted Age for Preemies

When people ask me how old my baby is, I sometimes find myself struggling to give them an answer. Sure, he was born on Mother’s Day this year and I’ve got a solid date on the calendar, but when it comes to preemie babies, the answer is a little more complex than that. Usually I respond with his chronological age (his age since his actual date of birth) but preemie babies also have to factor in their adjusted age as well.

Judah’s original due date was June 20 and he arrived at 34 weeks and three days on May 12. His chronological age puts him at nearly a month and a half old. However, his adjusted age makes him only ten days old today. So how does adjusted age work?


It’s pretty simple: take your baby’s chronological (actual) age in weeks and subtract from that the number of weeks premature that your baby was born. Here’s the handy formula:

Chronological Age (in Weeks) – Number of Weeks Premature = Adjusted Age

So in Judah’s case, he’s actually seven weeks old today, but he was born five weeks early, making his adjusted age only two weeks. It’s pretty crazy when you consider he’s been out in the world since May, yet his adjusted age only makes him two weeks old!

Why does adjusted age matter?
When a baby is born premature, determining their preemie age is important in understanding their milestones, since preemie babies typically achieve some milestones behind peers of their same chronological age. At the same time, some preemie babies can advance in certain milestones and early development than their peers by the virtue of arriving earlier. As such, adjusted versus chronological age can make confusing for parents when it comes to their child’s development.

Thankfully, pediatricians and neonatologists agree that preemie babies’ development tends to catch up and level off with their peers around age two.

No matter how old he is, we don’t take a single second with our son for granted and we keep our eyes peeled for every single developmental milestone. Fingers crossed, we get to see Judah’s first big developmental milestone very soon: a real smile!

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