BMI Calculator — Free

Body Mass Index (BMI) is a simple anthropometric calculation that uses your height and weight to estimate overall body mass. It is calculated by dividing weight in kilograms by the square of height in meters, or by dividing weight in pounds by the square of height in inches and multiplying by 703.

While it is not a direct measurement of body fat, it serves as a cost-effective clinical screening tool to identify potential weight categories that may lead to health problems. If you prefer a low-impact approach to improving your BMI, our walking weight loss calculator can show you how much weight you can lose through daily walking alone.

† Senior (65+) ranges come from observational geriatric research showing lower mortality at a slightly higher BMI; they are not official WHO or CDC thresholds. The calculator applies them automatically when age is 65 or over. For seniors it labels a BMI below 23 as “Below range” rather than “Underweight”, since a BMI in the high teens to low 20s can still be healthy at this age.

The WHO 2004 Expert Consultation defined two additional action points for Asian populations — increased risk at BMI 23.0 and high risk at BMI 27.5. The finer Asian obesity sub-class divisions (Class II at 32.5, Class III at 37.5) are applied here for consistency with the standard six-class structure and are not themselves WHO-defined cut-offs.

Body Mass Index (BMI) serves as a foundational screening tool for medical professionals to categorize individuals into weight groups. However, health thresholds can vary significantly across different populations. For South Asian descents, health organizations including the WHO BMI classification suggest adapted BMI thresholds.

For individuals of South Asian, East Asian or South-East Asian descent — including Indian, Pakistani, Bangladeshi, Chinese, Japanese and Korean populations — the WHO 2004 revised thresholds classify overweight from BMI 23.0 and obesity from BMI 27.5, reflecting higher metabolic risk at lower BMI values compared to European populations. To use this as an Asian BMI calculator, turn on the Asian descent toggle and these regional thresholds are applied to your result automatically.

The WHO 2004 thresholds are the same for Asian men and women — there is no separate Asian BMI formula for females. At any given BMI, women naturally carry a higher proportion of body fat than men, but the healthy ceiling of 22.9 and the 23.0 overweight action point apply to both sexes. An Asian female with a BMI of 23 is therefore flagged at increased metabolic risk under these thresholds even though the same value reads as “normal” on the standard WHO scale.

Metabolic profiles and structural physiology shift as we age, necessitating different interpretations of standard weight metrics. For older adults (over the age of 65), the standard WHO definition of "normal weight" (18.5–24.9) may actually be associated with higher mortality risks due to decreased physiological reserves.

Observational geriatric research indicates that a BMI in the 23–28 range often correlates with better health outcomes in older adults than the standard 18.5–24.9 band, providing a necessary buffer against illness-related weight loss and age-related muscle wasting (sarcopenia). Within that broader window, the lowest all-cause mortality is typically observed around 25–27 in the most comprehensive analyses to date. A landmark 2013 JAMA meta-analysis of 97 studies covering 2.88 million adults found that adults classified as overweight (BMI 25–30) had significantly lower all-cause mortality than those in the normal-weight range. That analysis was not stratified by age, but the protective buffer it describes — against illness-related weight loss and sarcopenia — is particularly relevant for older adults.

Using a standard BMI calculator immediately following childbirth can yield highly misleading results. During early postpartum recovery, your body retains significant excess fluids, increased blood volume, and structural tissue adaptations from pregnancy.

Clinical guidelines from ACOG recommend waiting until you have fully completed the acute postpartum recovery phase (typically 6–12 weeks) before assessing baseline body mass metrics, as early measurements do not accurately reflect true adipose tissue levels.

The Department of Defense (DoD) utilizes BMI as an initial screening tool for medical readiness and physical fitness evaluations. However, military personnel frequently exceed standard BMI limits due to increased lean muscle mass from rigorous training protocols.

According to military medical standards, service members who fail the initial BMI screening are advanced to secondary body composition assessments—typically the circumference tape test—to directly estimate body fat percentage rather than relying solely on the height-to-weight ratio.