About the Child BMI Calculator
Use this tool to check a child or teen aged 2 to 19 years against the CDC 2000 BMI-for-age growth charts. You enter sex, age (years and months) and height and weight in metric or imperial units. The page runs entirely in your browser; nothing uploads to a server and no account is needed. The calculator converts height and weight to BMI, then uses the CDC LMS values to produce a z-score and percentile. It also shows a healthy BMI range for that age, the 95th percentile BMI, percent of the 95th, and obesity class per AAP/CDC rules. Results update as you type and you can copy the output or share a link that reopens with the same numbers. Results are estimates and not medical advice; a doctor reviews growth over time before making a diagnosis.
How to use it
- 1Enter sex: Male or Female.
- 2Enter exact age in years and months.
- 3Choose units: Metric or US and UK.
- 4Type weight and height (decimals or inches and feet accepted).
- 5Copy the result or use the share link to reopen with the same numbers.
Worked example
Input: Female, age 10 years 0 months, Metric, weight 32 kg, height 140 cm. Result shown: BMI = 16.3. The tool then shows BMI-for-age percentile, z-score, healthy BMI range, 95th percentile and percent-of-95th using CDC 2000 charts.
The formula
BMI = weight (kg) / height (m)^2Then compare BMI with children of the same sex and exact age in completed months using the CDC 2000 BMI-for-age growth charts and LMS parameters: z = ((BMI / M)^L - 1) / (L × S)Percentile = normal distribution of zFor BMI above the 95th percentile the tool uses the CDC 2022 extended percentiles: 90 + 10 × normal((BMI - P95) / sigma)CDC groups used: under 5th percentile = underweight; 5th to below 85th = healthy weight; 85th to below 95th = overweight; 95th and above = obesitySevere obesity (class 2) = 120% of the 95th percentile or BMI ≥ 35Class 3 = 140% of the 95th percentile or BMI ≥ 40Source: CDC Growth Charts and Child and Teen BMI CalculatorCDC Growth Chart data files (LMS parameters). Last checked 5 November 2026.
What it is good for
- Runs fully in your browser; no upload or account required.
- Shows BMI, percentile, z-score, healthy range and percent-of-95th in one view.
- Instant updates as you type and a shareable link for later review.
- Covers ages 2 to 19 years only and uses CDC 2000 charts.
- BMI is a screening estimate, not a direct measure of body fat or a medical diagnosis.
Questions people ask
What ages does this calculator cover?
The tool covers children and teens aged 2 to 19 years using the CDC 2000 BMI-for-age growth charts. For infants younger than 2 years use WHO length/weight standards or consult your clinician.
Which units can I use?
You can use Metric (kg and cm) or US and UK (lb, ft and in). Enter exact age in years and months for the most accurate percentile.
How fast do results update?
Results update instantly as you type. There is no calculate button. You can copy the numbers or create a share link that reopens with the same inputs.
What does the percentile mean?
The BMI-for-age percentile compares the child to a reference population of the same sex and exact age. For example, the 50th percentile is the population median. Categories follow CDC cutoffs: under 5th underweight, 5th to <85th healthy weight, 85th to <95th overweight, 95th and above obesity.
Can I use this to diagnose a health problem?
No. The results are estimates and not medical advice. BMI screens for weight concerns; a doctor looks at growth patterns, medical history and body composition before diagnosing.
What method does the calculator use to get a percentile?
The calculator uses BMI = weight(kg)/height(m)^2 and converts BMI to a z-score and percentile with CDC 2000 LMS parameters. For very high BMIs it applies the CDC 2022 extended percentiles.
Is my data stored or shared?
The calculator runs client-side in your browser, so nothing is uploaded by default. You can copy results or create a share link that encodes the numbers in the URL.
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