Is a baby at the 10th percentile underweight?

Not necessarily. The 10th percentile means your baby weighs more than 10% of babies the same age and sex. If they've been consistently around the 10th percentile, they're likely following their own healthy growth curve. A sudden drop from the 50th to the 10th would be more concerning.

Do premature babies use the same growth charts?

WHO charts use chronological age. For premature babies, your pediatrician may use corrected age (adjusting for weeks of prematurity) for the first 2–3 years. Ask your doctor which age to use when tracking at home.

Why did my baby's percentile change between visits?

Small shifts (5–10 percentile points) between visits are normal. Babies don't grow at a perfectly steady rate — they have growth spurts and slower periods. Only sustained changes across multiple visits are significant.

Are growth charts different for breastfed and formula-fed babies?

The WHO charts were built from data on healthy, breastfed children. Breastfed babies tend to gain weight faster in the first 3–4 months and slower after that compared to formula-fed babies. This is normal — the WHO charts account for this pattern.

Can I use Babylitics to share growth data with my pediatrician?

Yes. You can generate a secure, time-limited link or QR code to share your baby's growth charts and measurements. Your pediatrician doesn't need a Babylitics account — they just open the link.

How to Read Your Baby's Growth Chart (Percentiles Explained)

You've just left the pediatrician's office and heard something like: "Your baby is at the 35th percentile for weight." Is that good? Bad? Should you worry? Here's what growth chart percentiles actually mean, how to read them, and when a number truly matters.

What Is a Baby Growth Chart?

A growth chart is a graph that plots your baby's weight or length against a reference population of healthy children of the same age and sex. The curved lines on the chart represent percentiles — each line shows where a certain percentage of children fall.

The WHO Child Growth Standards were developed from a study of 8,440 healthy, breastfed children across six countries — Brazil, Ghana, India, Norway, Oman, and the United States.

Source: WHO (2006)

These charts are the global standard for children from birth to 5 years. Your pediatrician uses them at every well-child visit.

What Do Percentiles Mean?

A percentile tells you how your baby compares to other healthy babies of the same age and sex. If your baby is at the 40th percentile for weight, it means:

40% of healthy babies weigh less
60% of healthy babies weigh more

Important: a percentile is not a grade. Being at the 20th percentile is not "failing" and being at the 90th is not "winning." What matters is consistency — your baby following their own curve over time.

Percentile Range	What It Means
3rd–15th	Lower end of normal — healthy if consistent
15th–85th	Middle range — where most babies fall
85th–97th	Higher end of normal — healthy if consistent
Below 3rd or above 97th	May warrant closer monitoring

What's the Difference Between WHO and CDC Growth Charts?

This causes a lot of confusion. Here's the simple version:

The CDC recommends using WHO growth charts for children under 2 years of age and CDC charts for children aged 2 to 20 years.

Source: CDC (2010)

WHO charts (2006) describe how children should grow under optimal conditions — breastfed, healthy, well-nourished. They are a prescriptive standard.

CDC charts (2000) describe how American children actually grew based on historical survey data. They are a descriptive reference.

For babies under 2, both the CDC and the WHO recommend using the WHO standards. Babylitics uses WHO charts for all weight and length tracking.

When Should I Worry About My Baby's Percentile?

A single percentile number at one point in time tells you very little. What matters is the trend over multiple measurements. Watch for these red flags:

Crossing two or more percentile lines in either direction over a few months
Falling below the 3rd percentile for weight or length
A sudden plateau or drop in an otherwise steady curve
Weight and length diverging significantly (e.g., weight dropping while length stays the same)

The AAP recommends weight checks at each well-child visit — typically at 1, 2, 4, 6, 9, 12, 15, 18, and 24 months of age.

Source: AAP (2024)

One measurement that looks off is rarely cause for alarm. Two or three in a row that show the same trend is worth discussing with your pediatrician.

How Often Should I Measure My Baby?

For weight, the AAP recommends measurements at each well-child visit. Between visits, weekly or biweekly weigh-ins are sufficient. Daily weighing can cause unnecessary anxiety because normal fluctuations in hydration and feeding can swing the number day to day.

For length, measurements are less frequent — typically at well-child visits only, since accurately measuring a squirming baby at home is difficult.

How Does Babylitics Help Me Track Growth?

Babylitics plots every measurement you log directly on the WHO percentile curves. You'll see:

Your baby's data points connected as a line on the growth chart
WHO percentile bands from the 3rd to the 97th percentile
The median line (50th percentile) for reference
Growth velocity — how fast your baby is gaining weight or length over time
Gender-specific charts — WHO standards differ for boys and girls

You don't need to calculate anything. Log a measurement and see exactly where your baby stands — the same view your pediatrician uses, available on your phone anytime.

Frequently Asked Questions

Plot your baby's weight and length against WHO growth curves — free for 15 days, no credit card required.

Start tracking growth today