BMI Calculator
Body Mass Index is a quick screening number based on your height and weight. Enter both to see your BMI and which category it falls into. It is a useful general indicator, not a complete picture of your health.
Your BMI sits in the range linked with the lowest health risk. Keep up the habits that got you here — regular movement, hydration, and good sleep.
BMI is a general screening number and does not account for muscle mass or body composition. Treat it as one signal among many.
How it's calculated
BMI = weight (kg) ÷ height (m)²
Your weight in kilograms divided by the square of your height in metres. In imperial units the same result comes from weight (lb) ÷ height (in)² × 703. The output is a single number that estimates whether your weight sits in a healthy range for your height — a screening figure, not a body-composition scan.
What your result means
These ranges come from the World Health Organization and apply to most adults aged 20 and over. Children, athletes, and older adults are read differently — see the notes below.
| Category | BMI range | What it means |
|---|---|---|
| Underweight | Below 18.5 | May point to under-nutrition or low muscle mass. Worth raising with a doctor if it is unintentional. |
| Healthy weight | 18.5 – 24.9 | Associated with the lowest weight-related health risk for most adults. |
| Overweight | 25.0 – 29.9 | A raised long-term risk of heart disease and type 2 diabetes. Small, steady habit changes move the needle. |
| Obese | 30.0 and above | A higher risk of weight-related conditions. A doctor can help you build a realistic, sustainable plan. |
Why BMI matters
BMI is the fastest, cheapest way to flag a weight-related health risk worth a closer look. It does not diagnose anything, but a number well outside the healthy range is a useful prompt to check in with a doctor or rethink a few daily habits.
What BMI doesn't tell you
BMI cannot see the difference between fat and muscle, so very muscular people often read as 'overweight' while being extremely fit. It also ignores where fat sits on your body, your age, and your ethnicity — all of which change real risk. Treat it as one signal among many, alongside waist measurement, energy levels, and how you actually feel.
How to lower your BMI safely
If your goal is to bring the number down, aim for slow and steady: a small, consistent calorie deficit, more daily movement, strength work to protect muscle, and enough sleep. Crash diets drop the number fast and rebound just as fast. One to two pounds a week is a sustainable target for most people, and building in more daily movement is one of the easiest places to start.
Frequently asked questions
Is BMI an accurate measure of health?
BMI is a useful general screening tool, but it does not account for muscle mass, body composition, or fitness. A muscular athlete and a sedentary person can share the same BMI. Treat it as one signal among many — not a verdict.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is considered the healthy range and carries the lowest weight-related health risk. Below 18.5 is underweight, and 25 or above is overweight.
Why do muscular people get a high BMI?
Muscle is denser and heavier than fat, so people who lift weights or play sport often weigh more for their height and score as 'overweight' despite having low body fat. For very muscular bodies, body-fat percentage or waist measurement is a better guide.
Is BMI the same for men and women?
The BMI formula and category ranges are identical for adult men and women. Women naturally carry more body fat at the same BMI, so the number is best read alongside other measures rather than on its own.
Does BMI work for older adults?
In adults over about 65, a slightly higher BMI (roughly 23–28) is sometimes linked to better outcomes, partly because some extra reserve helps during illness. Muscle loss with age can also make BMI underestimate body fat. Use it as a rough guide and talk to a doctor about your individual targets.
How quickly can I safely lower my BMI?
Losing one to two pounds (about 0.5–1 kg) per week is the widely recommended safe pace. That usually means a modest calorie deficit plus more movement. Faster loss tends to cost you muscle and rebound once normal eating resumes.
What's the difference between BMI and body fat percentage?
BMI estimates risk from height and weight alone. Body fat percentage measures how much of your body is actually fat versus muscle, bone, and water. Body fat percentage is more precise but needs special tools to measure, while BMI needs only a scale and a tape.