---
title: "Baby Growth Charts: How to Read Weight, Length and Percentiles"
description: "How to read your baby's growth chart (WHO standards): what a percentile means, how much weight babies gain per month, why the 3rd percentile can be as healthy as the 97th, and which curve changes deserve attention."
canonical: https://buppi.baby/en/blog/baby-growth-chart-percentiles/
last-updated: 2026-10-14
---

# Baby Growth Charts: How to Read Weight, Length and Percentiles

> How to read your baby's growth chart (WHO standards): what a percentile means, how much weight babies gain per month, why the 3rd percentile can be as healthy as the 97th, and which curve changes deserve attention.
>
> Canonical: https://buppi.baby/en/blog/baby-growth-chart-percentiles/

Few things generate as much checkup anxiety as a loose sentence about percentiles: "she's at the 15th." Is that high? Low? Is it a grade? Breathe: **a percentile is not a ranking, and a growth chart is not a test**. It's a map — and this guide teaches you to read the map the way the pediatrician does: what a percentile is, how much babies actually gain per month, why a stable 3rd percentile can be perfectly fine, and which movements on the curve genuinely deserve attention.

## What the chart is (and what it isn't)

The curves used in checkups worldwide (and in Brazil's Child Health Booklet) are the **WHO growth standards**, built by following thousands of healthy, breastfed babies across six countries. They describe **how healthy babies grow**, by age and sex, across four main measures: **weight**, **length/height**, **head circumference** and **BMI**.

What the chart is **not**:

- **Not a target**: the 50th percentile isn't "the right one" — it's just the middle of the distribution.
- **Not a grade**: the 97th isn't "better" than the 15th.
- **Not a diagnosis**: an isolated point says little; the **trajectory** says much more — read together with gestational age, clinical history and measurement quality.

## Percentiles, translated

Being at the **25th percentile for weight** means: out of 100 healthy babies of the same age and sex, ~25 weigh less and ~75 weigh more than yours. That's all.

The right question is never "what percentile is she at?" but "**is she following her own channel?**". A baby living and growing at the 10th can be as healthy as one at the 85th — each on their own track, **as long as** the trajectory, the proportions between measures and the clinical exam agree (the final word always belongs to the checkup).

And a timeline detail that prevents scares: **in the first months, size reflects intrauterine life more than genetics**. The "family channel" is typically found between 6 and 24 months, through physiological **catch-up** (babies born small accelerating) or **catch-down** (big babies decelerating) adjustments — channel crossings **in that window and context** can be perfectly normal, and the pediatrician is who tells them apart from a problem.

## How much babies actually gain

Practical clinic ranges (bedside rules used in well-child care — the WHO publishes detailed *velocity* tables by sex and interval, with much wider dispersion; the fine reading is always the pediatrician's):

| Phase | Typical weight gain | Length |
| --- | --- | --- |
| Week 1 | physiological loss (see note below) | — |
| Week 2 to month 1 | ~25 to 35 g/day from the lowest point — month 1 is the most intense (the WHO median tops 800 g for the month) | ~3.5 to 4 cm in the month |
| 1 to 3 months | ~700 to 900 g/month (20–30 g/day) | ~3 to 3.5 cm/month |
| 3 to 6 months | ~450 to 600 g/month | ~2 cm/month |
| 6 to 9 months | ~300 to 450 g/month | ~1.5 cm/month |
| 9 to 12 months | ~200 to 400 g/month | ~1.2 cm/month |

**About week 1**: physiological loss exists, but it has a ruler — losses **above ~7%** usually prompt a closer evaluation of latch and feeds (according to age in days and clinical context), and **above 10%**, further evaluation without delay; regaining birth weight is expected by day 10–14. The "chart" daily gain counts **from the lowest point** (the nadir), not from birth weight.

Two readings that calm things down:

- **The slowdown is expected**: the baby didn't "stop growing well" at 8 months — the whole curve decelerates. As a population approximation (not an individual target), birth weight usually **triples** in the first year and length grows ~50% — almost all of it concentrated in the first half.
- **Head circumference has its own curve** and matters as much as weight — it's brain growth measured from the outside. The interpreter is always the pediatrician.

## The curve movements that deserve attention

The curve becomes an investigation topic when the **trajectory** changes, not when the number is "low" or "high". The patterns the pediatrician watches closely:

- **Sustained downward line-crossing**: the classic clinical reference is crossing **two major lines** of the chart (e.g., from the 50th to below the 15th, heading toward the 3rd) — a signal for evaluation, not a diagnosis.
- **Stalling**: zero gain between weigh-ins in the first months is active investigation — a young baby doesn't wait 30 days flat for someone to look.
- **Measures detaching**: weight dropping with length preserved (or the reverse), or head circumference leaving its channel — each combination tells a different story.
- **Very fast climbing** is also a conversation: crossing channels upward in the first year, especially on formula, calls for a look at volumes and responsive feeding.

And the counterpoint that prevents scares: **small, transient dips happen** — an illness the week of the weigh-in, a different scale, a full diaper. An isolated point is rarely a trend — what counts is the pattern across visits. Hence the golden rule: compare **the whole curve**, never two isolated weigh-ins.

## Preterm babies: another curve, another age

For premature babies, **plotting chronological age on the standard curve creates false alarms**: **corrected age** is used (discounting the weeks missing to 40) on the WHO curves — generally until age 2 — and, in the neonatal period, preterm-specific curves (such as Intergrowth-21st or Fenton), depending on the service. If your baby was born early, the curve reading is its own chapter of the checkup — always ask which age and which curve are being used.

A technical detail that changes numbers: until age 2, **length is measured lying down** (afterwards, standing height — which reads ~0.7 cm less), and measuring a squirming baby carries real error — one more reason not to compare measurements from different sources.

## Weighing at home: less is more

The temptation to weigh every week (or every day) is understandable — and counterproductive:

- Different scales vary between themselves more than a week's gain.
- Diaper, a recent feed and time of day shift tens or hundreds of grams.
- The result is anxiety without information: the trend that matters shows up over **weeks and months**, at checkups, with the same scale and technique.

The real exception: when the pediatrician requests closer weight monitoring (a newborn struggling to gain, for example) — then it's with their guidance, technique and scale.

## The booklet (or the chart at your clinic) is the curve's home

In Brazil, the curve lives in the **Child Health Booklet (Caderneta da Criança)** — the Ministry of Health document every baby receives at the maternity ward, with the WHO curves printed for recording weight, length, head circumference and BMI at every visit; elsewhere, your pediatrician's chart plays the same role. Three golden habits: **bring it to every visit**, check that the points were plotted, and photograph the pages now and then (backup).

> **See the pediatrician without waiting for the next routine visit if**: the baby clearly stopped gaining weight, lost weight outside the first week of life, wet diapers decreased along with it, or the baby seems listless and feeding much less. The curve is a monitoring tool — acute signs don't wait for the next dot on the graph.

## The graph only works with points — log between visits

The official curve is drawn at checkups, but the context that explains each point — how feeds, sleep and diapers went in those weeks — is what turns "dropped half a channel" into either a quick diagnosis or a discarded false alarm. Logging the routine day to day (feeds, diapers, sleep, and weight when the pediatrician asks) arrives at the visit as the full story behind the graph.

## FAQ

### What does my baby's percentile mean?

The percentile compares your baby with the WHO reference for the same age and sex: being at the 25th percentile for weight means that, out of 100 healthy babies, about 25 weigh less and 75 weigh more. It's not a grade or a ranking: the 3rd and the 97th can be equally healthy. What the pediatrician assesses isn't the isolated number, but whether the baby follows their OWN growth channel across visits. (In Brazil's Child Health Booklet the same curve also appears as z-scores — formal diagnoses use the -2 and -3 standard-deviation cutoffs; percentile and z-score are two rulers for the same map.)

### How much weight does a baby gain per month?

As a practical clinic rule (the WHO publishes detailed velocity tables, with wide dispersion): month 1 is the most intense (median above 800 g); from 1 to 3 months, about 700 to 900 g per month (20 to 30 g/day); 3 to 6 months, 450 to 600 g per month; 6 to 9 months, 300 to 450 g; 9 to 12 months, 200 to 400 g. The slowdown through the year is expected and healthy. Remember the physiological loss of the first week (above ~7% usually prompts a closer look at feeding, and above 10%, further evaluation without delay), typically regained between days 10 and 14 — and daily gain counts from the lowest point.

### My baby is in the 10th percentile. Should I worry?

A stable low percentile is usually just that baby's size — genetics counts a lot, especially after 6 months (before that, the intrauterine environment weighs more). What deserves investigation isn't being at the 10th, but crossing percentile lines downward in a sustained way, stopping weight gain, or weight detaching from length. The one who separates normal variation (including the physiological catch-up/catch-down adjustments between 6 and 24 months) from a problem is the pediatrician, with the full curve in hand.

### Do formula-fed babies grow differently from breastfed ones?

The WHO standards were built with breastfed babies — that's the growth considered ideal. Observational studies show formula-fed babies tend, on average, to gain weight somewhat faster in the second half of the year — a group tendency, not an individual rule — which reinforces responsive feeding (respecting fullness) so the tendency doesn't become excess. The reference curve used is the same for everyone.

### How often should I weigh and measure my baby?

At routine checkups. Weighing at home every week (or every day) creates more anxiety than information: daily fluctuations from diapers, feeds and different scales deceive. The months-long trend is what matters — different scales on different days aren't comparable. The real exception: when the pediatrician asks for more frequent weight checks (a newborn struggling to gain, for example) — then it's with their guidance, technique and scale.

### What about premature babies?

Preterm babies get their own reading: plotting chronological age on the standard curve creates false alarms. Corrected age (discounting the weeks missing to 40) is used on the WHO curves — generally until age 2 — and, in the neonatal period, preterm-specific curves (like Intergrowth-21st or Fenton), depending on the service. If your baby was born early, always ask which age and which curve are being used.