30 October 20269 min read

Baby Growth Percentiles: What Your Baby's Chart Means

Medical Review

Medically Reviewed by Dr. Pedro Yelamo Vera, MD

Licensed Physician No. 484814280 · Official Medical College of Bizkaia (Spain)Last reviewed: 31 October 2026

Baby growth percentiles explained: what the lines mean, which chart Spain, the UK and the US use, and when a change in percentile needs a check.

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Baby growth percentiles compare your baby's weight, length and head size with healthy babies of the same age and sex. The 50th percentile is the middle. Any line between the lowest and highest curves is normal. What matters most is the pattern over time: a baby who keeps growing along a similar curve is usually doing well.

TL;DR

A percentile is a ranking, not a score. The 25th percentile means 75 in 100 babies of that age are bigger.
Spain has no single chart. Many regions use Fundación Orbegozo charts; some use WHO charts.
The UK red book uses UK-WHO charts. In the US, the CDC advises WHO charts until age 2 and CDC charts after.
One measurement means little. A steady drop across two or more lines needs a check.
Use corrected age for premature babies until age 2.

Dr. Pedro Yelamo Vera is a GP licensed in Spain (Colegiado No. 484814280).

For a medical emergency, call 112 or go to the nearest local emergency department. Do not wait for a video consultation or an online reply.

What does a percentile mean on a baby growth chart?

A percentile (or centile) shows where your baby sits among 100 healthy babies of the same age and sex. On the 50th percentile, half of babies weigh more and half weigh less. On the 3rd percentile, only 3 in 100 are smaller.

A high or low number is not good or bad on its own. Small parents often have small, healthy babies. Spain's paediatric association (AEP) says growth depends mostly on genes and sex. A baby on the 9th percentile who stays near it is usually fine.

Charts track weight (peso), length (longitud, later talla) and head size (perímetro cefálico).

Which percentile range is normal?

It depends on the chart, so check which one your report uses.

Spain: the AEP describes the usual normal range as between the 3rd and 97th percentile. Some healthy children still grow below the 3rd.
UK: the red book shows lines from the 0.4th to the 99.6th centile. The RCPCH says only 4 in 1,000 healthy children are below the 0.4th, and they should be checked.
US: on WHO charts the CDC flags a weight-for-length below the 2nd or above the 98th percentile, and a length below the 2nd.

These lines do not prove a problem. They tell the doctor when to look closer.

Which growth charts are used in Spain, the UK and the US?

The same baby can sit on a different line on a different chart. This often confuses families who move.

WHO standards. They come from about 8,500 healthy children in six countries, followed from birth to age 5. The breastfed baby is the model.
Spain. There is no single national chart. A 2015 study in Anales de Pediatría found most regions used the Fundación Orbegozo charts. Valencia, Andalusia and Navarra used WHO charts in the child health booklet. The authors found clinically important differences between the two and called for one shared chart.
UK. The red book uses the UK-WHO charts, based on the WHO standards, up to age 4.
US. The CDC advises WHO charts from birth to age 2, then CDC charts from 2 to 20. A child's percentile can drop when they switch charts at age 2, without any real change.

Feeding matters too. The CDC notes that from about 3 months, breastfed babies usually gain weight more slowly than formula-fed babies. So a formula-fed baby may drift up on WHO charts. If the line jumps after a move, ask which chart was used, and bring the red book to your Spanish visit.

Worried about your baby's weight, feeding or a change on the growth chart?

You can book a video visit with a GP licensed in Spain, in English or Spanish. He goes through the chart with you, asks about feeding and nappies, and helps you decide on next steps with your paediatrician.

See available times

When should a change in percentile worry you?

A single measurement means little. Scales differ, and babies wriggle when measured. The trend is what counts.

Moving one line up or down is common. The AEP notes that between 6 and 18 months, some healthy children settle onto a new percentile.
Crossing two or more lines is less common. The NHS advises talking to your health visitor. The RCPCH says a lasting drop of this size happens in fewer than 2 in 100 babies and needs a check.
A short dip during illness is normal. Weight usually catches up within 2 to 3 weeks.

Weighing too often causes needless worry. The NHS suggests no more than once a month up to 6 months. In Spain, your baby is weighed at the routine revisiones del niño sano.

Is it normal for a newborn to lose weight?

Yes, some loss in the first days is normal. The NHS says most babies are back at birth weight by 3 weeks. The RCPCH advises a check and a feeding review if a baby loses 10% or more.

How do you read the chart for a premature baby?

Use corrected age: the age your baby would be if born at 40 weeks. A baby born at 28 weeks is 12 weeks early, so at 6 months the corrected age is 3 months. The AEP advises this for growth until age 2.

What is BMI-for-age, and when does it start?

From age 2, doctors can plot body mass index (BMI, IMC) by age. In the US, the CDC calls the 85th percentile and above overweight, and the 95th and above obesity. It calls BMI a screening tool, not a diagnosis. Spanish charts may give a different result.

When should you see a doctor about your baby's growth?

See a doctor today, without waiting, if your baby:

Is not feeding normally.
Has fewer wet nappies than usual, which can mean dehydration.
Is quiet, floppy, hard to wake or unusually sleepy.
Has green vomit.

Call 112 if your baby stops breathing, will not wake up, or has a rash that does not fade when you press a glass on it. If your baby is under 6 months old and you are very worried, go to urgencias. Trust your instincts.

Talking it through with a doctor by video

Dr. Yelamo is a GP licensed in Spain. He sees adults, children and pregnant patients by video, every day from 07:30 to 20:30 (Spain time). In the visit he will:

Look at the growth chart with you and check which chart and age were used.
Ask about feeding, wet nappies, sleep and how your baby is developing.
Tell you if your baby needs to be weighed and examined in person, and by whom.

He does not promise any test or prescription before the visit. Where clinically appropriate, following a genuine evaluation. Treatment and prescriptions are issued solely at the doctor's discretion based on evidence-based clinical guidelines.

A prescription is never guaranteed: it is issued only where clinically appropriate after a genuine evaluation, as a private electronic prescription under Spanish law. This service is for urgent, non-emergency care. In an emergency, call 112.

See how the Urgent Care video visit works. It lasts 15 minutes and costs €50.

This guide is general information. It does not replace a check-up with your child's paediatrician.

Frequently asked questions

Is the 10th percentile bad for a baby?

No. A baby on the 10th percentile is smaller than 90 in 100 babies of the same age and sex, and that is within the normal range. What matters is whether the baby keeps growing along a similar curve, feeds well and is developing normally.

Is a 95th percentile baby overweight?

Not on its own. Under age 2, doctors look at weight compared with length, not weight alone. On WHO charts a weight-for-length above the 98th percentile is flagged for a closer look, and a long baby can be heavy and healthy.

How much percentile change is normal?

Moving up or down by one centile line is common. Crossing two or more lines is less common and is worth discussing with your child's nurse or doctor, especially if the drop continues.

Why did my baby's percentile drop after I moved to Spain?

Often because the chart changed. Spain has no single national chart: many regions use the Fundación Orbegozo charts and some use the WHO charts. Different charts can place the same baby on a different percentile.

When is a baby's weight an emergency?

Weight alone is rarely an emergency. Call 112 if your baby stops breathing, will not wake, or has a rash that does not fade under a glass. See a doctor today if your baby is not feeding or has fewer wet nappies.

Sources

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This content is written and reviewed by a licensed physician with reference to the following official health authorities.