Body Mass Index (BMI) is a simple screening tool that estimates whether your weight is healthy for your height. At your annual doctor's visit, they ask your height and weight, and within seconds they know if you're underweight, normal weight, overweight, or obese—that's BMI in action. It's fast, free, and requires just two measurements, which is why it's used globally by doctors, public health organizations, and fitness professionals. But BMI is also misunderstood: many people think it measures body fat (it doesn't), or that it's a diagnosis (it's not). It's simply a screening flag that tells you whether your weight-to-height ratio falls into a healthy range statistically linked to lower disease risk.
A BMI of 25 is the cutoff between "normal weight" and "overweight," but this single number means different things depending on your body composition. A muscular athlete might have a BMI of 27 (classified as overweight) but be in excellent health with low body fat. Conversely, someone with a BMI of 23 (normal range) might have higher body fat if they're sedentary. So while BMI is useful for population-level screening, it's imperfect for individuals. Still, for most people, BMI is a reasonable starting point: if your BMI is 30+, that's usually a signal to talk with a healthcare provider about lifestyle changes, not because the number itself is magical, but because a high BMI statistically correlates with health risks like diabetes, heart disease, and certain cancers.
This BMI calculator shows you your index, your weight category, and the healthy weight range for your height. Use it as a general guide, not a diagnosis. If you're concerned about your health or weight, consult a healthcare professional who can assess your individual circumstances—including muscle mass, fitness level, age, and family history—rather than relying on a single number.
How BMI is calculated
BMI uses your weight and height with this formula:
BMI = weight (kg) ÷ [ height (m) ]²
For imperial units the calculator converts feet/inches and pounds to metric first,
then applies the same formula, so the result is identical either way. The result is interpreted the same regardless of units, which is why BMI is used globally in medical practice.
What your BMI tells you (and what it doesn't)
Your BMI score falls into one of several categories that correlate with health risks at the population level. A high BMI statistically increases risk for type 2 diabetes, heart disease, high blood pressure, and joint stress. A low BMI can indicate insufficient calorie intake, malnutrition, or underlying illness. But BMI is a screening tool, not a diagnosis. Two people with the same BMI can have very different body compositions: one might be muscular, the other might have high body fat. Age matters too—a BMI of 24 might be ideal for a 30-year-old but concerning for an 80-year-old. Pregnancy, athletic training, and medical conditions all affect the interpretation of BMI.
cm
kg
Your BMI
24.2
Normal weight
Healthy weight range (for your height)
53.5–72.0 kg
BMI Categories & What They Mean
BMI categories are based on statistical associations with health risks. Your BMI is calculated as weight (kg) ÷ height (m)². Below are the ranges and what each typically indicates.
UnderweightBMI < 18.5
Typically indicates insufficient weight for your height. Can indicate malnutrition, illness, or naturally low weight. Health risks include weak immune function, osteoporosis, and anemia. Consult a healthcare provider if unexpectedly underweight.
Normal WeightBMI 18.5–24.9
The statistically healthiest range for most adults. Associated with lowest risk for weight-related diseases (diabetes, heart disease). This is the target range for most people. Maintain with balanced nutrition and regular activity.
OverweightBMI 25–29.9
Above healthy range; increased risk for weight-related health issues. May not yet cause problems, but is a signal to monitor health markers (blood pressure, cholesterol, blood sugar). Lifestyle changes can prevent progression to obesity.
ObeseBMI ≥ 30
Significantly elevated health risks. Associated with type 2 diabetes, heart disease, high blood pressure, joint stress, and certain cancers. Medical intervention and lifestyle changes are recommended. Consult a healthcare provider for personalized guidance.
⚠️ Important Limitations:
Doesn't measure body fat: Muscle tissue weighs more than fat, so athletes may have high BMI despite low body fat.
Doesn't account for age: Recommendations differ for children, adults, and seniors.
Doesn't account for body composition: Two people with the same BMI can have very different health profiles.
Use as screening, not diagnosis: BMI is a population-level screening tool, not a medical diagnosis. Consult a healthcare provider for personalized assessment.
What your result means
Under 18.5 — Underweight
18.5 – 24.9 — Normal weight
25 – 29.9 — Overweight
30 and above — Obese
The "healthy weight range" shown is the span of weights that would place you in the normal-BMI band for your current height.
Frequently asked questions
What is BMI?
Body Mass Index (BMI) is a simple ratio of weight to height (kg ÷ m²). It is a quick screening tool to estimate whether a person is underweight, normal weight, overweight, or obese.
What are the BMI categories?
For adults: below 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese.
Is BMI accurate for everyone?
BMI does not distinguish muscle from fat, so it can misclassify very muscular people, and it is interpreted differently for children, pregnant women and the elderly. Use it as a general guide, not a diagnosis.
How do I lower my BMI?
BMI falls when weight decreases relative to height, generally through a sustainable combination of balanced nutrition and regular physical activity. Consult a healthcare professional for personalised advice.
For general information only — not medical advice.
