Premature babies often grow differently to full-term babies, particularly in the early weeks when weight, feeding, and development are closely monitored.
Once feeding is established, many premature babies begin to gain weight steadily — often in small daily increases that build over time. While growth can feel slow at first, this early progress forms the foundation for later catch-up growth.
Growth can feel slow at first, especially when changes are measured in grams rather than visible size — but this is how healthy progress is tracked in premature babies.
Many preterm babies move closer to typical growth ranges by around 12 to 24 months, although this varies depending on how early they were born and their individual needs.
How to use this guide
If you're looking for a quick answer, the summary section below gives typical growth ranges.
If you want to understand what to expect over time, the growth timeline and corrected age sections will be most helpful.
What Is Normal Growth for a Premature Baby?
In the early stages, growth is carefully monitored — especially in the NICU — to ensure a baby is gaining weight and developing safely.
Once feeding is established and a baby is medically stable, premature babies typically gain:
- Around 15–20 grams per kilogram of body weight per day
- In some cases, slightly higher targets may be used depending on how early a baby was born
It is also normal for premature babies to lose some weight after birth (often around 7–10%). This can feel concerning, but it is expected. Most babies begin to regain this weight steadily and typically return to their birth weight within 2–3 weeks.
In the early weeks, progress is often measured in grams rather than visible size, which is why changes can feel slow even when growth is on track.
Typical Growth at a Glance
- Weight gain: ~15–20g per kg per day
- Initial weight loss: ~7–10% after birth
- Birth weight regained: ~2–3 weeks
- Catch-up growth: commonly within 12–24 months
- Corrected age used until: around 2 years
Premature Baby Growth Timeline
Understanding how growth typically progresses can help provide some structure during what can feel like an uncertain time.
First few weeks
- Initial weight loss followed by gradual regain
- Feeding is established and monitored
- Growth may feel slow but is closely tracked
0–3 months (corrected age)
- More consistent weight gain begins
- Babies gradually become stronger
- Early physical development becomes more noticeable
3–12 months (corrected age)
- Growth often becomes more visible
- Some babies experience periods of faster "catch-up" growth
- Body proportions begin to even out over time
12–24 months
- Many premature babies move closer to typical growth ranges
- Catch-up growth often becomes more evident during this period
This is why growth can feel gradual at first, even when progress is happening as expected. As babies grow, they gradually move through different clothing sizes — you can read more about this in our guide on when premature babies move into newborn sizes.
Understanding Corrected Age (Why It Matters)
Corrected age (also called adjusted age) is one of the most important concepts when understanding premature baby growth.
It reflects your baby's development based on their due date, rather than their birth date.
Simple example:
- A baby is 4 months old
- They were born 2 months early
- Their corrected age is 2 months
This means growth and development should be compared to a 2-month-old, not a 4-month-old.
Not sure what your baby's corrected age is? Use our corrected age calculator — enter your baby's birth date and gestation for an instant result.
In the UK, healthcare professionals use corrected age when:
- Monitoring growth
- Assessing development
- Tracking milestones
Corrected age is typically used until around 2 years of age, when many premature babies have caught up.
Common Misunderstanding about Premature Baby Growth
It's easy to compare a premature baby's progress to full-term babies of the same age. However, growth and development should always be viewed using corrected age in the early years.
Without adjusting for prematurity, a baby may appear behind when they are actually progressing as expected.
How Premature Baby Growth Is Measured
In the UK, premature baby growth is tracked using UK-WHO growth charts developed by the RCPCH (Royal College of Paediatrics and Child Health), which are specifically designed for monitoring babies born early.
These charts allow healthcare professionals to track growth over time and assess whether a baby is following a consistent pattern, rather than focusing on individual measurements.
These charts measure:
- Weight
- Length (height)
- Head circumference
Rather than focusing on a single number, healthcare teams look at:
- Overall growth trends
- Consistency over time
- Whether a baby is following their own pattern
It is common for premature babies to begin on lower centiles, particularly in the early months.
These charts are not used to compare your baby to others, but to ensure they are growing consistently along their own curve. Growth is usually reviewed regularly by healthcare teams to ensure progress remains steady over time.
Premature Baby Milestones (Using Corrected Age)
Developmental milestones are assessed using corrected age and are best viewed as a general guide rather than a fixed timeline.
Premature babies may reach these slightly later than full-term babies, but they typically follow a similar pattern over time.
Around 1–2 months (corrected age)
- Making eye contact
- Beginning to smile
- Small head movements during tummy time
Around 4 months
- Stronger head control
- Grasping objects
- Increased vocal sounds and interaction
Around 6 months
- Rolling over
- Sitting with support
- Reaching and transferring objects between hands
Around 9 months
- Sitting independently
- Beginning to crawl or move
- Babbling sounds
Around 12 months
- Pulling to stand
- Taking early steps or cruising
- Using simple words
What Affects How Fast a Premature Baby Grows?
-
Gestational age at birth
Babies born earlier often need more time to catch up. -
Birth weight
Smaller babies may grow at a different pace initially. -
Feeding and nutrition
Consistent feeding plays an important role in steady growth. -
Medical needs
Some babies may grow more slowly while recovering or adapting. -
Individual variation
Each baby follows their own growth pattern, even within similar circumstances.
When Do Premature Babies Catch Up?
Many premature babies experience catch-up growth between 12 and 24 months. You can read more about this in our guide on when premature babies catch up in size.
By around age 2:
- A large proportion of babies are within typical growth ranges
- Development is often aligned with peers when measured using corrected age
Some babies — particularly those born very early or with lower birth weights — may take longer, sometimes up to 2–3 years.
Catch-up growth is gradual and best understood over time rather than week by week.
Understanding Your Baby's Growth Journey
Premature baby growth rarely follows a perfectly smooth pattern. It is common to see periods where progress feels slower, followed by phases where growth becomes more noticeable — particularly as feeding improves and babies become stronger.
In clinical practice, growth is assessed using tools such as UK-WHO charts and corrected age to ensure that progress is viewed in the right context. This allows healthcare professionals to focus on long-term trends rather than short-term changes.
While many premature babies reach similar growth ranges to their peers within the first two years, the timing can vary depending on factors such as gestational age and early health needs.
Understanding how premature babies grow — and what to expect over time — can make it easier to interpret your baby's progress.
If growth appears to slow significantly or feeding becomes difficult, healthcare professionals may review progress more closely.
Continue learning about premature baby care
- Free premature baby calculators — size finder and corrected age tool
- Preemie clothing size guide
- How to dress a premature baby safely
- How many preemie clothes do you need
- Premature baby clothes
This guide is part of our premature baby care knowledge hub. You can also read Theo's story to understand the experience behind Simply Preemie.
This guide is for general information only and is not a substitute for professional medical advice. If you have any concerns about your baby's growth or development, please speak with your GP, health visitor, or neonatal care team.Written by Rachael, founder of Simply Preemie and mum to Theo, born at 28 weeks.
