Calculate your Body Mass Index and health category
BMI stands for Body Mass Index. It is a number calculated from your height and weight that gives a quick snapshot of whether your body weight is in a healthy range for your height. Doctors and health professionals use it as a starting point for health assessments because it is fast, free, and requires no special equipment.
The formula is simple: divide your weight in kilograms by the square of your height in metres. For example, if you weigh 70 kg and are 1.75 m tall, your BMI is 70 divided by (1.75 x 1.75), which equals 22.9 — a healthy weight range.
This can indicate insufficient nutrition, underlying illness, or an unusually fast metabolism. Being underweight carries health risks including weak bones, poor immune function, and fatigue. A doctor or dietitian can help identify the cause and suggest a plan.
This is the healthy range. People in this category have a statistically lower risk of heart disease, diabetes, and certain cancers. Maintaining this range through balanced eating and regular activity is the goal for most people.
Being in this range means you are carrying more weight than is ideal for your height. The health risks are moderate at this stage — increased risk of high blood pressure, high cholesterol, and type 2 diabetes. Lifestyle changes like regular walking and reducing processed food intake can bring the number down significantly.
Obesity significantly raises the risk of serious health conditions including heart disease, stroke, sleep apnea, type 2 diabetes, and joint problems. A BMI in this range is a strong indicator to consult a healthcare provider for a personalised health plan.
BMI is a useful screening tool, but it has real limitations you should know about:
Bottom line: Use BMI as one data point among many. Always combine it with waist circumference measurements, blood test results, and a conversation with your doctor for a complete picture.
Use BMI as a baseline measurement when starting a new diet or exercise routine. Track it monthly to see progress.
Many medical forms ask for your BMI. Calculate it beforehand so you're prepared for doctor or insurance forms.
If you know your height, you can calculate the weight range that would give you a healthy BMI and use that as your target.
Parents use BMI tracking alongside growth charts to ensure children are developing at a healthy rate.
Many workplace wellness programs use BMI as one of the metrics to track employee health and wellbeing.
Athletes track BMI alongside other metrics like body fat percentage to optimise performance and weight class eligibility.
BMI is a useful starting point for most adults but it has well-documented limitations. It is not accurate for highly muscular people, pregnant women, children (who use separate charts), or elderly individuals who have lost muscle mass. It also does not account for ethnic differences in body composition. For a complete health assessment, doctors use BMI alongside waist measurements, blood pressure, blood sugar, and cholesterol levels.
For most adults aged 18 to 65, a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight. Between 25 and 29.9 is overweight. A BMI of 30 or above falls into the obese category. These ranges were established by the World Health Organisation and are used by healthcare systems worldwide as a standard reference point, though some organisations suggest slightly different ranges for different ethnicities.
Yes, and this is sometimes called "normal weight obesity" or being "skinny fat." A person can have a BMI in the normal range but still carry a dangerously high percentage of body fat concentrated around the abdomen. This increases risk of metabolic disease even when BMI looks fine. This is why doctors also measure waist circumference and check blood markers like blood sugar and cholesterol in addition to BMI.
For general health monitoring, checking your BMI once a month is usually sufficient. If you are actively trying to lose or gain weight, checking every two to four weeks gives you enough time between measurements to see meaningful changes without obsessing over daily fluctuations. Body weight naturally shifts by one to two kilograms throughout each day based on hydration, meals, and activity, so taking measurements under consistent conditions — such as first thing in the morning — gives the most reliable trend data.
The same BMI formula and categories apply to both men and women, but the underlying body composition at any given BMI number differs significantly between sexes. Women naturally carry more body fat than men at the same BMI due to hormonal differences. A woman with a BMI of 22 may have 25% body fat while a man with the same BMI might have 18%. This does not mean the formula is wrong, but it does mean that body fat percentage measurements give a more accurate picture of health for both men and women.
You can work this out from BMI. For a healthy BMI range of 18.5 to 24.9, multiply both numbers by your height in metres squared. For example, if you are 1.70 m tall, your height squared is 2.89. A healthy weight range would be 18.5 times 2.89 (53.5 kg) to 24.9 times 2.89 (71.9 kg). So for a 1.70 m person, a weight between 53 and 72 kg is in the healthy BMI range. Use our calculator above to find your personal range instantly.
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