How do I calculate my child's BMI?

First convert height into meters and calculate BMI as weight in kilograms divided by height in meters squared. For children, that is only the first step. The raw BMI value must then be compared with CDC BMI-for-age reference data for the child's age and sex. A kids BMI calculator automates both steps so families do not need to compute the number and then manually look up the percentile on a separate chart.

What is a healthy BMI for a 10-year-old?

There is no single healthy BMI number that fits every 10-year-old because children's body composition changes with age and differs by sex. A more useful answer is the BMI percentile. In CDC screening, a BMI percentile from the 5th up to the 85th percentile is usually described as the healthy weight range. Even then, one number still needs context from height percentile, growth history, puberty timing, activity level, and family build.

What BMI percentile is considered overweight for a child?

On CDC BMI-for-age charts, a percentile from the 85th percentile up to but not including the 95th percentile is generally labeled overweight, while the 95th percentile and above is in the obese range. Those labels are screening categories rather than diagnoses. A child may still need a fuller clinical assessment before anyone decides whether weight truly reflects excess body fat, medical risk, or a temporary shift during growth or puberty.

Is a BMI of 17 healthy for a child?

It depends on the child's age and sex. A BMI of 17 could be very typical for one age and much less typical for another because child BMI is never interpreted with adult rules. That is why a child BMI percentile is more meaningful than the raw BMI value alone. If you enter the child's age, sex, height, and weight into the calculator, you can see whether BMI 17 lands in a healthy weight range for that specific stage of growth.

Why is my child's BMI percentile different from their weight percentile?

Weight percentile and BMI percentile measure different things. Weight percentile compares body weight with peers of the same age and sex, while BMI percentile also considers standing height. A child can have a typical weight percentile but a higher BMI percentile if height is relatively lower, or a lower BMI percentile if height is relatively higher. That is why BMI-for-age is often more useful than weight alone when screening for weight-related risk.

Can a child have a high BMI but still be healthy?

Yes. BMI is a screening tool, not a diagnosis. A muscular child, a child in a rapid pubertal transition, or a child with a naturally larger frame can show a higher BMI percentile without having the same health risk as another child with similar BMI. That is why pediatric interpretation should also consider activity, diet quality, waist pattern, family history, and whether the BMI change is persistent or just a temporary part of growth.

What is the difference between child BMI and adult BMI?

Adult BMI uses fixed numeric cutoffs such as 18.5, 25, and 30. Child BMI does not, because normal body fat changes with age and differs between boys and girls. For children aged 2 to 20 years, BMI is interpreted as a percentile on sex-specific CDC growth charts. The same BMI value can therefore mean different things at different ages, which is why a child BMI percentile is the correct standard instead of adult BMI categories.

How accurate is a BMI calculator for kids?

The math itself is very accurate when the height, weight, age, and sex inputs are correct and when the calculator uses official BMI-for-age reference data. The limitation is interpretation rather than arithmetic. BMI does not directly measure body fat, so it can overestimate or underestimate risk in some children. It is most accurate as a first-pass screening tool that identifies when a fuller clinical assessment may be worth discussing.

What should I do if my child's BMI is above the 95th percentile?

A BMI percentile above the 95th percentile is a reason to talk with a pediatric clinician, but it is not a reason to panic. The next step is usually to confirm height and weight, review the growth trend across several visits, and consider sleep, activity, nutrition, medications, puberty stage, and family history. The goal is not to react to one number in isolation, but to understand whether the pattern is persistent and clinically meaningful.

Does BMI change during puberty for kids?

Yes. Puberty can shift BMI percentile because height, body fat, and lean mass do not change at the same speed. Girls often show a normal rise in body fat during puberty, which can raise BMI percentile, while boys often gain more lean mass and may show a different pattern. A short-term percentile change during puberty is not unusual, but a sustained shift should still be interpreted with the broader growth chart and clinical context.

At what age can I start using a BMI calculator for my child?

BMI-for-age screening is generally used from age 2 through age 20. Below age 2, clinicians usually rely on weight-for-length rather than BMI because infant body proportions are different and the CDC BMI-for-age framework is not intended for that range. This page therefore starts at 24 months. For babies and younger toddlers, a baby growth chart or weight-for-length reference is the more appropriate tool.

BMI Calculator for Kids

This BMI calculator for kids uses CDC growth standards to calculate BMI-for-age percentiles for children aged 2 to 20 years. Unlike adult BMI, children's BMI is interpreted by age and sex. Enter your child's measurements below for instant results.

✓ CDC BMI-for-age percentiles (ages 2-20)
✓ Separate reference ranges for boys and girls
✓ Plain-language interpretation included
✓ No sign-up — all results stay in your browser

BMI Calculator for Kids

This embedded calculator starts at age 2, defaults to CDC BMI-for-age standards, and highlights BMI percentile before the rest of the growth metrics so families can immediately see the screening category.

How to Read Your Child's BMI Result

Below P5

Underweight range. Discuss persistent low BMI with a clinician.

P5-P85

Healthy weight range for BMI-for-age screening.

P85-P95

Overweight risk zone. Trend and clinical context matter.

Above P95

Obese risk zone. Pediatric follow-up is recommended.

BMI is a screening tool, not a diagnosis. Age, sex, puberty stage, and clinical context still matter.

Percentile results

Current percentile summary

Using: CDC

Loading percentile data…

Interactive charts

Visualize the current percentile position

Chart type

Metric

Loading chart data…

What Is BMI-for-Age and Why It Differs from Adult BMI

BMI-for-age means body mass index is first calculated as BMI = weight(kg) / height(m)^2 and then compared with CDC reference data for children of the same age and sex. That second step is what makes child BMI different from adult BMI. Adults use fixed cutoffs such as 18.5, 25, and 30. Children do not, because normal body fat changes throughout growth and because boys and girls develop differently. A child BMI percentile therefore tells a more accurate story than a raw BMI number alone. This is also why BMI is not routinely used below age 2; infants are usually evaluated with weight-for-length rather than BMI-for-age. For the broader standards explanation behind that cutoff, read the WHO vs CDC growth chart guide.

How to Interpret Your Child's BMI Percentile

A child BMI percentile is a screening category rather than a diagnosis. In CDC BMI-for-age charts, below the 5th percentile is considered underweight, the 5th to 85th percentile is usually described as a healthy weight range, the 85th to 95th percentile is an overweight range, and the 95th percentile or higher is an obese range. Those categories are helpful because they organize risk, but they do not replace clinical judgment. A muscular child, a child in a fast growth spurt, or a child in puberty can all show a different BMI pattern than expected from one snapshot alone. If you want the broader concept primer before focusing only on BMI, read BMI percentile explained.

BMI percentile	Category	Meaning
Below P5	Underweight	Lower BMI-for-age screening range. Persistent readings deserve medical review.
P5-P85	Healthy Weight	Typical BMI-for-age screening range for most children.
P85-P95	Overweight	Higher-than-expected BMI range that should be interpreted in context.
P95+	Obese	Higher-risk screening range where pediatric follow-up is recommended.

Healthy BMI Range for Kids by Age — Reference Chart

A healthy BMI range for kids is not one fixed number. It changes with age and it changes by sex. That is why normal BMI for children by age is best shown in percentile rows instead of an adult-style chart with just one acceptable window. The tables below focus on the most practical screening lines: P5, P50, P85, and P95. Many parents search for one healthy BMI number, but the better question is where the child sits relative to these age-specific thresholds and whether the same child is tracking in a stable way over time.

Boys BMI-for-Age CDC

CDC BMI-for-age reference rows

Age	P5	P50	P85	P95
2 years	14.7	16.6	18.2	19.3
3 years	14.3	16	17.4	18.3
4 years	14	15.6	16.9	17.8
5 years	13.8	15.4	16.8	17.9
6 years	13.7	15.4	17	18.4
8 years	13.8	15.8	17.9	20
10 years	14.2	16.6	19.4	22.1
12 years	15	17.8	21	24.2
14 years	16	19.1	22.6	26
16 years	17.1	20.5	24.2	27.5
18 years	18.2	21.9	25.6	28.9
20 years	19.1	23	27	30.6

Girls BMI-for-Age CDC

CDC BMI-for-age reference rows

Age	P5	P50	P85	P95
2 years	14.4	16.4	18	19.1
3 years	14	15.7	17.2	18.3
4 years	13.7	15.3	16.8	18
5 years	13.5	15.2	16.8	18.2
6 years	13.4	15.2	17.1	18.8
8 years	13.5	15.8	18.3	20.7
10 years	14	16.8	19.9	22.9
12 years	14.8	18.1	21.7	25.2
14 years	15.8	19.3	23.3	27.2
16 years	16.8	20.4	24.6	28.9
18 years	17.5	21.3	25.7	30.3
20 years	17.8	21.7	26.5	31.8

Reference values from CDC 2000 Growth Charts. BMI percentile thresholds: Underweight <P5, Healthy P5-P85, Overweight P85-P95, Obese P95+.

BMI Percentile for Boys vs Girls — Key Differences

Boys and girls do not use the same BMI chart because body composition changes differently across childhood and adolescence. The same BMI value can map to a different percentile depending on sex and age. Girls often show a normal rise in body fat during puberty, which can increase BMI percentile even when growth is healthy. Boys often add more lean mass through puberty, so a BMI rise may reflect a different body composition pattern. That is why this page keeps separate BMI reference rows for boys and girls and why a child BMI percentile should never be interpreted without age and sex.

What Causes BMI Changes in Children?

Not every BMI change means a health problem. Normal causes include a height spurt that temporarily lowers BMI, a slower height phase that makes BMI look higher, puberty-related changes in body composition, or seasonal shifts in appetite and activity. Short-term illness can move weight quickly and change BMI before height catches up. The more important pattern is whether BMI is crossing major percentile channels over a sustained period. A repeated child BMI change matters more than one isolated jump because screening is strongest when it follows a trend instead of a single reading.

Limitations of BMI as a Health Measure for Kids

BMI has clear limitations in children. It does not separate muscle from fat, does not directly measure fat distribution, and does not capture fitness, sleep, diet quality, or underlying medical conditions. Different ethnic and genetic backgrounds can also affect body composition. That does not make BMI useless; it makes BMI a screening tool rather than a final answer. A higher or lower percentile should usually lead to better questions, not instant conclusions. When families ask whether BMI is accurate for kids, the practical answer is that it is useful for flagging patterns but incomplete as a stand-alone judgment.

When to Talk to a Doctor About Your Child's BMI

It is reasonable to contact a pediatric clinician when BMI is persistently below the 5th percentile or at or above the 95th percentile, when BMI changes rapidly across two major percentile channels, or when a visible change in appetite, energy, sleep, exercise tolerance, or mood appears at the same time. It is also helpful to ask for advice when growth, puberty timing, and BMI no longer seem to fit together. Screening tools are designed to identify these moments. They do not replace clinical care, but they do help families know when extra context and medical interpretation would be useful.

Frequently Asked Questions About BMI for Kids

These questions address common search intents around child BMI calculation, healthy BMI ranges by age, and how to interpret CDC BMI-for-age percentile results.

A BMI calculator for kids uses age, sex, height, and weight to estimate BMI-for-age percentile. That percentile shows how a child's BMI compares with other children of the same age and sex rather than using one fixed adult cutoff. The tool is most useful as a screening aid because it quickly flags whether BMI trends lower, typical, or higher than expected and whether follow-up with a pediatric clinician may be helpful.

Related Growth Chart Tools

Boys Growth Chart Girls Growth Chart Baby Growth Chart 0-24m Toddler Growth Chart Growth Percentile Guide WHO vs CDC Charts

BMI Calculator for Kids

BMI Calculator for Kids

What Is BMI-for-Age and Why It Differs from Adult BMI

How to Interpret Your Child's BMI Percentile

Healthy BMI Range for Kids by Age — Reference Chart

Boys BMI-for-Age CDC

Girls BMI-for-Age CDC

BMI Percentile for Boys vs Girls — Key Differences

What Causes BMI Changes in Children?

Limitations of BMI as a Health Measure for Kids

When to Talk to a Doctor About Your Child's BMI

Frequently Asked Questions About BMI for Kids

What is a BMI calculator for kids?−

How do I calculate my child's BMI?+

What is a healthy BMI for a 10-year-old?+

What BMI percentile is considered overweight for a child?+

Is a BMI of 17 healthy for a child?+

Why is my child's BMI percentile different from their weight percentile?+

Can a child have a high BMI but still be healthy?+

What is the difference between child BMI and adult BMI?+

How accurate is a BMI calculator for kids?+

What should I do if my child's BMI is above the 95th percentile?+

Does BMI change during puberty for kids?+

At what age can I start using a BMI calculator for my child?+

Related Growth Chart Tools