BMI Calculator

BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared (kg/m2). The World Health Organization (WHO) classification for adults is: Under 18.5 — Underweight; 18.5 to 24.9 — Healthy weight; 25.0 to 29.9 — Overweight; 30.0 and above — Obese (with further sub-classifications of 30.0-34.9 moderate obesity, 35.0-39.9 severe obesity, and 40+ very severe obesity). A healthy BMI of 18.5-24.9 is associated with lower risk of cardiovascular disease, type 2 diabetes, and many other health conditions. However, BMI is a population-level screening tool and does not provide a complete picture of individual health. It does not distinguish between fat mass and muscle mass, or account for where fat is distributed in the body. The Ministry of Health NZ uses the WHO classifications as the standard reference point. Source: Ministry of Health NZ (health.govt.nz); World Health Organization (who.int).

New Zealand's Ministry of Health recognises that standard WHO BMI cut-offs may not be equally appropriate for all ethnic groups. For Asian populations, the Ministry recommends lower BMI cut-offs (23+ for overweight and 27.5+ for obesity) because Asian people tend to have a higher proportion of body fat at the same BMI as European populations, meaning health risks occur at lower BMI values. For Māori and Pacific peoples, the evidence is more nuanced. Some research suggests Pacific peoples tend to have greater lean muscle mass and bone density on average, meaning the standard WHO cut-offs may overestimate obesity prevalence and associated health risk in these populations. However, Māori and Pacific peoples in NZ still experience disproportionately high rates of obesity-related conditions including type 2 diabetes, cardiovascular disease, and certain cancers. Health professionals in NZ are advised to use BMI alongside other measures such as waist circumference when assessing individual patients. Source: Ministry of Health NZ (health.govt.nz).

BMI is a useful and widely used population-level screening tool, but it has well-documented limitations as an individual health indicator. BMI does not distinguish between fat mass and lean muscle mass — an elite athlete with very high muscle mass may have a BMI in the "overweight" range despite having low body fat. Conversely, someone with a healthy BMI may have high visceral fat (fat around internal organs), which carries significant health risks. BMI also does not account for age, sex, or ethnic differences in body composition. Research increasingly shows that waist circumference or waist-to-height ratio are better predictors of cardiovascular risk and metabolic disease than BMI alone. The Ministry of Health NZ recommends using BMI alongside waist circumference as a practical clinical screening approach. A waist circumference above 88 cm for women or above 102 cm for men indicates elevated health risk, regardless of BMI. BMI is not diagnostic — further clinical assessment is always needed. Source: Ministry of Health NZ (health.govt.nz).

According to the New Zealand Health Survey, approximately 34% of NZ adults (aged 15 and over) are classified as obese (BMI 30+), making New Zealand one of the highest-ranked OECD countries for adult obesity. A further 34% are classified as overweight (BMI 25-29.9), meaning about two-thirds of NZ adults are above the healthy weight range. Obesity rates have been rising steadily since the 1990s, driven by changes in diet, physical activity, food environments, and socioeconomic factors. Māori and Pacific adults have significantly higher obesity prevalence than European/Other New Zealanders. Obesity is a major driver of preventable health conditions including type 2 diabetes, cardiovascular disease, and some cancers, contributing substantially to health system costs. The Ministry of Health NZ tracks these trends through the annual NZ Health Survey. Addressing obesity is a key goal of Aotearoa NZ's health strategy. Source: Ministry of Health NZ — NZ Health Survey (health.govt.nz).