BMI Calculator

Work out your BMI, with Asian thresholds, child percentiles and the healthy weight range for your height.

Age group

Height

Weight

Age (optional)

Adds the notes that depend on age

BMI thresholds

StandardLower, for a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background

Enter your height and weight to see the result.

Underweight: WHO. Healthy weight and above: NICE NG246.

Add your waist: Waist-to-Height Ratio.

Works out your body mass index from your height and weight, places it in a band and gives the range of weights the calculator counts as healthy for your height, in the units you measure in. Adults can use the standard bands or the lower thresholds NICE sets for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background. For ages 2 to 19 it gives the BMI percentile from CDC's growth charts instead.

BMI is a screening number, not a diagnosis. Every calculation runs in your browser.

Understanding the result

For adults the bands are NICE's, with WHO's underweight below 18.5:

Standard — underweight below 18.5, healthy weight 18.5 to 24.9, overweight 25 to 29.9, obesity class 1 from 30, class 2 from 35 and class 3 from 40.
Lower thresholds — healthy weight 18.5 to 22.9, overweight 23 to 27.4, obesity from 27.5, with classes 2 and 3 from 32.5 and 37.5. People with these backgrounds are prone to fat around the middle and face cardiometabolic risk at a lower BMI.

Healthy weight for your height is every weight the calculator itself would put in the healthy band, rounded inward to 0.1 kg or a whole pound. When your BMI is outside the band, the line under it says how much weight reaches its nearer end.

BMI does not tell fat from muscle or say where fat sits. NICE advises reading it with caution in people with a lot of muscle and in people aged 65 and over, when a slightly higher BMI may be protective, and pairing it with the waist-to-height ratio below a BMI of 35. The 2025 Lancet Commission on clinical obesity likewise treats BMI as a first screen, to be confirmed with a waist measure or a direct measure of body fat. BMI does not apply in pregnancy.

For children and teens, the percentile is the share of children of the same age and sex in CDC's reference whose BMI is lower. Below the 5th percentile is underweight, the 85th to below the 95th overweight, the 95th and above obesity, and 120% of the 95th percentile and above severe obesity. The band is read from the BMI against those cut-offs, so a BMI just under the 95th percentile is overweight even when its percentile rounds to 95.0. The NHS uses the UK-WHO charts instead, with the 91st and 98th centiles, so a UK result there can differ; Indian paediatricians use the IAP charts.

How it works

BMI is worked out exactly from the weight and height you enter, then shown and banded at one decimal, halves rounding up: a BMI of 24.95 shows as 25.0 and is overweight. Pounds and inches convert exactly (1 lb = 0.45359237 kg, 1 in = 2.54 cm).

A child's age is counted in completed months as CDC counts them: the days from the date of birth to the date measured, divided by 30.4375, an average month, and rounded down. So 31 January to 28 February is 0 months, and the count can fall a day either side of a calendar month. CDC gives one row a month, and the row for those months is used as it stands. Up to the 95th percentile the percentile comes from the 2000 LMS curves; above it, from CDC's 2022 extended method, which stays meaningful at very high BMI. The percentile is shown to one decimal, between “< 0.1” and “> 99.9”.

BMI = weight (kg) ÷ height (m)²

Healthy weight: 18.45 × height² ≤ weight < 24.95 × height² (22.95 on the lower thresholds)

Up to P95: z = ((BMI ÷ M)^L − 1) ÷ (L × S), percentile = Φ(z) × 100

Above P95: percentile = 90 + 10 × Φ((BMI − P95) ÷ σ)

Examples

170 cm and 72.1 kg

72.1 ÷ 1.7² gives a BMI of 24.9, Healthy weight, at the very top of the healthy range of 53.4–72.1 kg for 170 cm on the standard bands. One more kilogram would show as 25.3, overweight.

170 cm and 70 kg on the lower thresholds

A BMI of 24.2 is healthy weight on the standard bands but overweight on the lower ones, whose healthy range for 170 cm is 53.4–66.3 kg. Losing 3.7 kg reaches it.

A girl of 9 years 6 months

With Child & teen, Female, Age from set to Years and months, 9 years and 6 months, 140 cm and 41.6 kg, the BMI of 21.2 is at the 92.2 percentile (z = 1.42): overweight. For an adult the same BMI would be healthy weight.

Healthy weight by height

The weights that give a healthy-weight BMI at each height, in kg, on both scales

Height	Standard	Lower thresholds
150 cm	41.6–56.1 kg	41.6–51.6 kg
155 cm	44.4–59.9 kg	44.4–55.1 kg
160 cm	47.3–63.8 kg	47.3–58.7 kg
165 cm	50.3–67.9 kg	50.3–62.4 kg
170 cm	53.4–72.1 kg	53.4–66.3 kg
175 cm	56.6–76.4 kg	56.6–70.2 kg
180 cm	59.8–80.8 kg	59.8–74.3 kg
185 cm	63.2–85.3 kg	63.2–78.5 kg
190 cm	66.7–90 kg	66.7–82.8 kg

Rules and sources

The adult bands are NICE NG246 recommendations 1.9.10 and 1.9.11 (2022, in the 2025 guideline). The lower thresholds apply to people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background; NICE identifies obesity classes 2 and 3 in these groups by taking 2.5 off the standard thresholds. Underweight below 18.5 is WHO's (TRS 894, Table 2.1).

The lower thresholds go back to a 2004 WHO expert consultation, which set public-health action points for Asian populations at 23 and 27.5 and left countries to choose their cut-offs. In India, the ICMR–National Institute of Nutrition's Dietary Guidelines for Indians (2024) use the same Asian cut-offs: overweight from 23 and obesity above 27.5. The calculator opens on the lower thresholds in South, East and South-East Asia, and on the standard bands elsewhere, since NICE's other groups are defined by background, which a location cannot tell.

Children and teens are read against CDC's BMI-for-age growth charts: the 2000 LMS curves up to the 95th percentile and the extended method published in December 2022 above it.

Sources

Overweight and obesity management (NG246), recommendations 1.9 and 1.10 — NICE
Obesity: preventing and managing the global epidemic (Technical Report Series 894), Table 2.1 — WHO
Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies (Lancet 2004;363:157–163) — WHO Expert Consultation
Dietary Guidelines for Indians 2024, Guideline 9 — ICMR – National Institute of Nutrition
Extended BMI-for-age growth charts: data files and method — CDC

Reviewed 20 October 2026

Frequently asked questions

On the lower thresholds, yes: overweight starts at 23 and obesity at 27.5, as NICE sets for people of South Asian background and India's Dietary Guidelines use. On the standard bands 23 is a healthy weight.

BMI counts all weight alike, so muscle raises it as fat does. NICE notes it is less accurate for people with a lot of muscle; the waist-to-height ratio, which NICE says holds for them too, is a better check of fat around the middle.

Both apply. The adult bands start at 18 and CDC's charts run to 19, so at those ages the calculator opens on the adult bands and offers the charts as well.