Body Mass Index (BMI)
Page updated: Evidence reviewed: What this means
Body mass index (BMI) is weight in kilograms divided by height in metres squared (kg/m²). It is a screening measure, not a direct measurement of body fat or a diagnosis of individual health.
These values reproduce the adult male and female percentiles in Table 10 of the June 2025 NCHS anthropometric report, based on measured NHANES August 2021-August 2023 data. Pregnant females were excluded from the published table. The 50th percentile describes the US population and is not a recommended target. Standard adult categories are Underweight below 18.5, Healthy Weight 18.5-24.9, Overweight 25.0-29.9, and Obesity 30.0 or higher. The WHO Asian expert consultation also identified lower BMI action points for many Asian populations. Read more on Wikipedia
Data source: Fryar et al. - NHANES Anthropometric Reference Data (2021 to 2023) About this study
Reference population: US adults aged 20 and over from the National Health and Nutrition Examination Survey (NHANES)
Body Mass Index (BMI) Norms Chart by Age and Sex (kg/m²)
| Age | Sex | Percentile | ||||
|---|---|---|---|---|---|---|
| 5th | 25th | 50th | 75th | 95th | ||
| 20-29 | Male | 18.9 | 23.3 | 27.0 | 31.1 | 39.6 |
| Female | 18.6 | 22.2 | 25.5 | 31.6 | 45.6 | |
| 30-39 | Male | 21.2 | 24.9 | 27.8 | 33.0 | 42.5 |
| Female | 19.7 | 24.2 | 28.6 | 35.2 | 47.4 | |
| 40-49 | Male | 22.2 | 25.7 | 28.9 | 33.5 | 45.0 |
| Female | 19.7 | 24.6 | 28.5 | 35.1 | 45.6 | |
| 50-59 | Male | 21.6 | 25.5 | 29.0 | 33.3 | 44.6 |
| Female | 20.8 | 24.9 | 30.0 | 36.5 | 45.9 | |
| 60-69 | Male | 21.2 | 25.2 | 28.3 | 32.1 | 39.9 |
| Female | 20.0 | 24.8 | 28.8 | 34.5 | 42.5 | |
| 70-79 | Male | 21.6 | 25.6 | 28.8 | 32.3 | 39.2 |
| Female | 20.7 | 24.7 | 28.0 | 33.4 | 42.2 | |
| 80+ | Male | 21.1 | 24.6 | 27.2 | 30.2 | 34.8 |
| Female | 19.2 | 23.6 | 26.9 | 31.3 | 36.3 | |
What to expect by age group
Among US adults in their 30s, the middle 50% measure a BMI of 24.9 to 33.0 for men and 24.2 to 35.2 for women. The median is 27.8 for men and 28.6 for women. Both are in the standard adult overweight category, but a population median is not an individual health target. BMI should be considered with other clinical and body-composition information.
| Age | Males | Females |
|---|---|---|
| 20-29 | 23.3 to 31.1 | 22.2 to 31.6 |
| 30-39 | 24.9 to 33.0 | 24.2 to 35.2 |
| 40-49 | 25.7 to 33.5 | 24.6 to 35.1 |
| 50-59 | 25.5 to 33.3 | 24.9 to 36.5 |
| 60-69 | 25.2 to 32.1 | 24.8 to 34.5 |
| 70-79 | 25.6 to 32.3 | 24.7 to 33.4 |
| 80+ | 24.6 to 30.2 | 23.6 to 31.3 |
Detailed Breakdowns
Select an age group and sex below for detailed percentile charts, tables, and ratings.
Frequently Asked Questions
What is a normal BMI?
The WHO defines normal weight as a BMI of 18.5 to 24.9. However, a WHO expert consultation (Lancet, 2004) found that Asian populations face higher health risks at lower BMI values, recommending action points of 23 for overweight and 27.5 for obesity. BMI alone does not account for muscle mass, bone density, or fat distribution.
How is BMI calculated?
BMI is calculated as weight in kilograms divided by height in metres squared (kg/m²). For example, a person weighing 70 kg who is 1.75 m tall has a BMI of 22.9. You can calculate yours using the CDC BMI calculator or the NHS BMI calculator.
Why is BMI controversial?
BMI does not distinguish between fat and muscle mass, so muscular athletes are often classified as overweight. It also does not capture fat distribution; abdominal fat carries more health risk than fat stored elsewhere. The standard WHO thresholds were developed primarily from European populations and may not apply equally across ethnic groups.
Why are the median BMI values so high?
The chart describes the measured US adult distribution in August 2021-August 2023. It is not a healthy-reference cohort, so its median should not be read as a target. BMI distributions also vary by country and population; NCD-RisC (Lancet, 2024) provides international context.