Baby Growth Chart UK: How to Track Your Newborn's Weight and Length in the First Year (2026)

Every single gram feels loaded in those first weeks. You leave the hospital, the midwife has circled a number in your red book, and suddenly that number becomes the most important thing in your world. Whether your baby has lost a little weight, whether they're on the "right" centile, whether they're keeping up — these thoughts can take over even the most laid-back new parent.

Here's the reassuring truth: a single number on a scale tells almost nothing on its own. What matters is the pattern of growth over time — and understanding how the UK's baby growth charts actually work puts you firmly in the driver's seat.

This guide walks you through exactly how RCPCH centile charts work, what healthy growth looks like month by month, when to speak to your health visitor, and how both parents can stay involved in tracking progress together.

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What Is the UK Baby Growth Chart?

In the UK, your baby's growth is tracked using UK-WHO growth charts — developed jointly by the Royal College of Paediatrics and Child Health (RCPCH) and the World Health Organisation. These charts live inside your baby's Personal Child Health Record, commonly known as the red book, which you'll receive after birth.

The UK-WHO charts are based on WHO Child Growth Standards, which describe optimal growth for healthy, breastfed children. There are separate charts for boys and girls, and specific charts for premature babies (more on that below).

Your health visitor or GP will plot your baby's weight, length, and head circumference on these charts at routine appointments — and they're also available digitally, with the RCPCH's tool used across many NHS Trusts.

What Are Centile Lines?

The curved lines running across the chart are called centile lines. They show how your baby's measurements compare with other babies of the same age and sex.

• A baby on the 50th centile sits right in the middle of the growth range
• A baby on the 25th centile is smaller than average but well within a healthy range
• A baby on the 75th centile is slightly larger than average — also completely normal

The UK-WHO charts include lines at the 0.4th, 2nd, 9th, 25th, 50th, 75th, 91st, 98th, and 99.6th centiles. The vast majority of babies — 99 out of 100 who are growing optimally — will fall somewhere between the outermost lines (the 0.4th and 99.6th centiles). Half of all babies will sit between the 25th and 75th centile lines.

The centile your baby sits on is far less important than whether they continue to follow a consistent line over time. A baby consistently at the 10th centile is just as healthy as one at the 90th, provided their growth is steady and their development is on track.

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The Red Book: Your Baby's Growth Companion

When you receive your red book, you'll notice the growth charts inside have no centile lines printed between birth and two weeks. That's intentional — the earliest days are a unique period, and health professionals interpret early measurements differently.

Your midwife will weigh your baby in the first week as part of their feeding assessment, and then again as needed. After the first two weeks, routine weighing for healthy babies typically follows this schedule:

• Once a month up to 6 months of age
• Once every two months from 6 to 12 months
• Once every three months after 12 months

Your baby will usually only be weighed more often than this if you ask for it or if there are concerns about their health or growth. Worth knowing: weighing your baby too frequently can sometimes cause unnecessary anxiety rather than provide reassurance.

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Newborn Weight in the First Days: What's Normal?

One of the most common surprises for new parents is that babies almost always lose weight in the first few days after birth. This is completely normal, and it reflects fluid loss and early feeding adjustments.

Most babies lose around 5–10% of their birth weight in the first three to five days. The key milestones to know:

• By around day 5–7: Weight loss typically peaks
• By 10–14 days: Most babies have returned to their birth weight
• By 3 weeks: The majority of babies are at or above their birth weight

If weight loss exceeds 10%, or if your baby hasn't regained their birth weight by around three weeks, a midwife or health visitor will give you extra support. They'll talk through how feeding is going and may observe a feed if you're breastfeeding.

The average birth weight for full-term babies in the UK is around 3.3–3.5 kg (7 lb 4 oz to 7 lb 11 oz), though a healthy range spans from roughly 2.5 kg to 4 kg. Newborn boys tend to be slightly heavier than newborn girls on average, though the difference is small.

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Baby Weight Gain Month by Month: A Rough Guide

Growth is never perfectly linear — babies have growth spurts, quieter patches, and the odd wobbly week. But here's a broad framework of what to expect across the first year:

Most babies double their birth weight by around 4–5 months and triple it by their first birthday. In the first month alone, most newborns gain around 450g–900g over their birth weight and grow approximately 2.5–4 cm in length.

As babies become more mobile — rolling, sitting, crawling — weight gain naturally slows. This is entirely expected and not a cause for concern in an otherwise healthy, active baby.

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What Growth Pattern Should You Look For?

This is the single most important point in this entire article: health visitors are far less concerned with the specific centile your baby sits on, and far more interested in whether they continue along a consistent growth line over time.

Your baby's weight may naturally go up or down by one centile line, and that's normal. It's less common — and worth flagging — if measurements cross two or more centile lines in either direction. If your baby's weight drops by two or more centile spaces and remains there, your health visitor will assess them more closely, including measuring their length.

A brief dip during illness is also normal. Babies may lose weight when unwell, but weight usually returns to their centile within two to three weeks.

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Breastfed vs Formula-Fed: Are Growth Patterns Different?

Yes — and the reason the UK-WHO charts were introduced in 2009 was specifically to address this. Previous UK growth charts were based predominantly on formula-fed babies, which set benchmarks that many breastfed babies couldn't meet — not because they were undernourished, but because breastfed and formula-fed babies simply have different, equally healthy, growth trajectories.

The current UK-WHO charts are based on the growth of breastfed infants, and are suitable for babies whether breastfed, formula fed, or having a mixture of both.

A few things worth knowing:

• In the first few months, formula-fed babies sometimes gain weight slightly faster than breastfed babies
• Breastfed babies tend to self-regulate their intake very well, which can result in leaner — but entirely healthy — growth patterns
• After around 6 months, growth rates between breastfed and formula-fed babies typically even out

If you're breastfeeding and your baby appears to be gaining weight more slowly than you expected, don't immediately assume something is wrong. Discuss the pattern with your health visitor rather than any single measurement.

If you want to connect feeding frequency with weight gain patterns — something that can feel like a guessing game in the early weeks — log your feeds on BumpSync. Tracking feeds alongside weight gives you a fuller picture, and makes conversations with your health visitor much more productive.

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Premature Babies and Growth Charts

If your baby arrived early, their growth is measured differently — and it's important to know this so you don't worry unnecessarily.

The UK-WHO charts include a separate preterm section for babies born between 32 and 36 weeks' gestation, and there is also a dedicated low birthweight chart for babies born before 32 weeks. Premature babies may grow in line with those born at term, but for some babies their growth and development may be slower — and that's accounted for in these specialist charts.

The key concept for premature babies is corrected age (also called adjusted age). This means your baby's age is calculated from their due date, not their birth date, when plotting on growth charts. So a baby born eight weeks early would have their measurements plotted eight weeks "behind" on the chart.

Your neonatal team and health visitor will use corrected age automatically, but if you're tracking your baby's growth yourselves, make sure you're using the same approach. Most health professionals continue using corrected age until a baby is around two years old.

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When to Flag Concerns to Your Health Visitor

Growth charts are a tool, not a verdict. The numbers don't exist in isolation — your health visitor will always look at the full picture: your baby's alertness, feeding, nappy output, and general wellbeing alongside the numbers.

That said, it's always right to seek advice if you notice:

• Weight loss exceeding 10% of birth weight in the newborn period
• Failure to regain birth weight by around three weeks
• Crossing two or more centile lines downward over time
• No weight gain over a two-week period (after the newborn phase)
• Your baby seems consistently unsatisfied after feeds or is feeding very poorly
• Your baby appears lethargic, unwell, or is vomiting frequently
• Feeding feels stressful, painful, or unmanageable

Trust your instincts as a parent. If something doesn't feel right, speak to your health visitor or GP — even if the numbers in the red book look fine. And equally, if the numbers cause you anxiety but your baby seems happy, alert, and feeding well, bring that to your appointment too. The full picture always matters more than the chart alone.

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Why Tracking Between Appointments Matters

Health visitor appointments are spaced out — rightly so, because too-frequent weighing can cause unnecessary worry. But that also means there can be weeks between data points, which can feel like a long time when you're in the thick of those early months.

This is where having your own record makes a real difference. Not to obsess over daily fluctuations (please don't do that!), but to arrive at each appointment with a clear, visual sense of your baby's trend — and to feel like an informed participant rather than someone waiting to be told what the numbers mean.

BumpSync's growth chart feature lets both parents log their baby's weight and length measurements and visualise them on a clean, easy-to-read chart between health visitor appointments. Rather than staring at the red book trying to interpret plotted dots, you can see your baby's growth trend at a glance — which takes a huge amount of the fear out of the numbers.

It's also a way for both partners to stay genuinely involved. When you can both see the same data, have the same context, and track the same trends, appointments feel collaborative rather than one partner fielding information and trying to relay it later.

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How Feeding Connects to Growth

Weight gain doesn't happen in a vacuum — it's directly linked to how and how often your baby feeds, especially in the early months. If weight gain slows, one of the first questions any health visitor will ask is about feeding: frequency, duration, latch, milk supply, or formula quantities.

Keeping a feed log — particularly in the first 12 weeks — is one of the most useful things you can do. It gives you data to share with your health visitor, helps you spot patterns (is your baby cluster feeding in the evenings? going longer stretches than before?), and removes a lot of the guesswork.

Log your baby's feeds on BumpSync to build a picture of feeding frequency and duration alongside weight measurements. When feeding data and growth data sit together, the patterns become much clearer — and so do conversations with your care team.

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Your Baby's Red Book: The Basics at a Glance

If you're new to the red book and its charts, here's a quick reference:

• What's in it: Weight, length/height, and head circumference charts, plus developmental review records
• Who plots it: Your midwife, health visitor, or GP
• How to read it: Find your baby's age along the bottom, their measurement up the side, and see which centile line (or gap between lines) they fall on
• What to look for: A consistent pattern tracking a similar centile over time — not a specific number
• Boys vs girls: Always use the sex-specific chart — using the wrong one gives inaccurate results
• Premature babies: Use corrected age, not chronological age, for plotting

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FAQ

What is a normal centile for a newborn in the UK?

There is no single "normal" centile. Any centile from the 0.4th to the 99.6th can be healthy. What matters is that your baby continues to grow along a consistent line rather than dropping or jumping significantly across centile spaces.

How much weight should a newborn gain each week?

In the first four months, babies typically gain around 150–200g per week. Between 6 and 12 months, this usually slows to around 85–140g per week. These are averages — individual babies vary, and short-term fluctuations are completely normal.

Should I weigh my baby at home between health visitor visits?

Most health guidelines suggest following the recommended weigh-in schedule unless there are specific concerns, as weighing too often can cause unnecessary anxiety. If feeding seems to be going well and your baby is alert and producing wet nappies, it's usually fine to wait for the scheduled appointment. If you're worried, speak to your health visitor rather than weighing daily at home.

My breastfed baby seems to be gaining weight more slowly than my friend's formula-fed baby. Should I be worried?

Not necessarily. Breastfed and formula-fed babies have different growth trajectories, and the UK-WHO charts are designed to reflect this. Breastfed babies often gain weight slightly more slowly in the early months while self-regulating their intake. Discuss the pattern with your health visitor rather than comparing to another baby.

How do growth charts work for premature babies?

Premature babies are plotted using their corrected age (adjusted from their due date, not their birth date), and there are specific preterm sections on the RCPCH charts for babies born between 32 and 36 weeks, as well as a separate low birthweight chart for those born before 32 weeks. Your neonatal team and health visitor will guide you through this.

When should I flag a concern to my health visitor about weight gain?

Contact your health visitor if your baby loses more than 10% of their birth weight, hasn't regained birth weight by three weeks, crosses two or more centile lines downward, or if something just feels off — even if you can't put your finger on exactly what. You know your baby best.

What does "crossing centile lines" mean?

It means your baby's weight or length measurements are moving significantly away from the centile line they've been tracking along. Moving up or down by one centile space is fairly common and usually fine. Crossing two or more centile spaces — particularly downward — is worth discussing with your health visitor.

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Track Growth Together, From Both Sides

In those early weeks, every weigh-in can feel like a judgement rather than just a data point. It doesn't have to feel that way — and having your own clear, visual record of your baby's growth pattern makes a real difference to how you walk into appointments.

Try BumpSync free and use the growth chart feature to log weight and length measurements, visualise trends, and connect feeding logs with growth patterns — all in one place that both partners can access. When the numbers feel less scary, appointments feel less like an exam and more like a conversation.

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Always speak to your midwife, health visitor, or GP if you have concerns about your baby's weight or growth. The information in this article is for general guidance only and is not a substitute for professional medical advice.