If your baby arrived early, you’ll quickly hear the term “corrected age” — and it can be confusing at first. It’s a simple, kind idea, though: it gives your baby credit for the weeks they spent growing outside the womb that a full-term baby spent inside. Here’s what it means and how to work it out.
What is corrected age?
Corrected age (also called adjusted age) is your baby’s age calculated from their original due date, not their birth date. A baby born eight weeks early has, in effect, an eight-week head start on the calendar that their body hasn’t “caught up” on yet — so measuring from the due date gives a fairer picture of where they are developmentally.
You’ll see two ages used side by side:
- Chronological age — the time since your baby was actually born, the age on the calendar.
- Corrected age — that age minus the number of weeks they were premature.
Both are correct; they just answer different questions. Birthdays and paperwork use chronological age, while development and growth are judged on corrected age. Holding both in mind at once takes a little getting used to, but it quickly becomes second nature.
How do you calculate corrected age?
The maths is straightforward:
- Work out your baby’s chronological age (time since birth).
- Work out how many weeks early they were born (40 weeks minus the weeks of pregnancy at birth).
- Subtract the weeks early from the chronological age.
For example, a baby who is 6 months old but was born at 32 weeks (8 weeks early) has a corrected age of about 6 months minus 8 weeks — roughly 4 months. If maths-while-sleep-deprived isn’t appealing, our baby age calculator does it for you when you enter the birth date and original due date.
When should you use corrected age?
Use corrected age whenever you’re looking at how your baby is developing or growing:
- Milestones — smiling, rolling, sitting, babbling and so on are expected around the corrected age, not the chronological one.
- Growth charts — weight, length and head circumference are plotted against corrected age so the percentiles make sense.
- Feeding and starting solids — readiness usually lines up better with corrected age in the first year.
So if your baby is four months old by the calendar but two months corrected, it’s the two-month milestones you’d gently look for — and there’s no need to worry that they’re “behind.”
How long does corrected age matter?
Most professionals use corrected age until around 2 years old. Premature babies do a remarkable amount of catching up over the first couple of years, and by age two the difference between corrected and chronological age usually makes little practical difference. Some follow it a little longer for babies born very early, which your provider will guide.
It’s worth remembering that catch-up isn’t a race. Some areas of development catch up faster than others, and your baby’s own pattern matters more than hitting a date. As they grow, our interactive milestone checklist can help you track skills — just read the ages as corrected ages while corrected age still applies.
What about babies born only slightly early?
For babies born a few weeks early — so-called “late preterm,” around 34 to 36 weeks — corrected age still applies, even though the gap is smaller. A two- or three-week head start sounds minor, but in the first few months it can be the difference between a milestone looking “late” and looking right on time. As a rule of thumb, if your baby was born three or more weeks before their due date, it’s worth using corrected age in the first year or two; for a baby born just a few days early, the adjustment is so small it rarely changes anything.
The earlier a baby is born, the more correcting matters and the longer it tends to be used. A baby born at 28 weeks has a 12-week correction, which is hugely significant at six months old, while the same correction barely registers by the time they’re two. This is exactly why the practice is to correct generously early on and then gradually let it go.
A gentle note for parents
The early arrival of a baby often comes with worry, and watching milestones can stir that up. Using corrected age is one small way to be fair to your baby and kind to yourself: it stops you comparing them to full-term babies who, in body-time, are simply older. Celebrate the progress you see, lean on your follow-up team for the bigger picture, and raise anything that concerns you — early support, when it’s needed, makes a real difference, and asking is always the right call.
Your baby has already done something extraordinary. Corrected age is just a tool to make sure the way you measure their growth honours that head start they had to make on their own. Keep it in your back pocket, use it whenever a chart or a milestone list quotes an age, and let it quietly fade once your little one has caught up — which, more often than not, they do.
This article is for general information only and isn’t medical advice. Premature babies often have specialist follow-up — for any question about your baby’s development, growth or corrected age, your healthcare provider is the best person to ask.