Your Body Mass Index (BMI) is one of the quickest ways to check whether your weight is in a healthy range for your height. Enter your height and weight below and this free BMI calculator will instantly show your BMI score, your weight category, and the healthy weight range for your height — no sign-up, no ads in the way, and your numbers never leave your browser.
This calculator is for adults aged 18–65. BMI is a screening tool, not a diagnosis — see the limitations section below.
How the BMI Calculator Works
Body Mass Index is a simple ratio of your weight to your height, first described by the Belgian statistician Adolphe Quetelet in the 19th century and later adopted by the World Health Organization (WHO) as a standard screening measure. The formula is the same everywhere: your weight in kilograms divided by the square of your height in metres. Because it only needs two measurements, BMI became the world’s most common first check for weight-related health risk — used by doctors, insurers, schools and public-health researchers alike.
Our calculator does the maths for you. It converts your entries to metric units if needed, applies the BMI formula, rounds the result to one decimal place, and matches it against the standard WHO categories. It also works backwards from your height to show the healthy weight range for someone of your stature, which is often more useful than the score alone: instead of an abstract number, you can see exactly how many kilograms sit between you and the healthy band.
How to Use This Calculator
- Choose your units — metric (centimetres and kilograms) or imperial (feet, inches and pounds).
- Measure your height without shoes, ideally in the morning when you are at your tallest.
- Weigh yourself on a flat, hard surface and enter your weight.
- Press Calculate my BMI and read your score, category and healthy weight range.
- Re-check every few months rather than every day — BMI is a long-term trend indicator, not a daily tracker.
BMI Categories Explained
The WHO categories for adults are: underweight below 18.5, normal (healthy) from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 or above, split into Class I (30–34.9), Class II (35–39.9) and Class III (40+). As BMI climbs above 25, the statistical risk of type 2 diabetes, cardiovascular disease, fatty liver and certain cancers rises steadily; below 18.5, risks include weakened immunity, bone loss and fertility problems.
A note on Asian cut-offs: research reviewed by the WHO found that people of South Asian and East Asian descent tend to develop weight-related conditions at lower BMI values, partly because of higher body-fat percentages and more abdominal fat at the same BMI. For these populations, many health authorities — including those in India, China, Japan and Singapore — use lower action points: overweight from 23 and obesity from 27.5. Our calculator flags this automatically whenever a result reaches 23, so you can judge your score against the cut-offs that fit your background.
Limitations of BMI
BMI is a population screening tool, and it has real limits for individuals. It cannot tell muscle from fat, so a strength athlete may score “overweight” while carrying very little body fat. It does not show where fat is stored, even though waist fat is riskier than hip fat. It also does not apply cleanly to children and teenagers (who need age- and sex-specific percentiles), to pregnant women, or to elderly people who have lost height. Treat your BMI as a starting point for a conversation about health — ideally alongside waist circumference, blood pressure, blood sugar and a proper check-up — never as a verdict on its own.
Frequently Asked Questions
What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. If you are of South or East Asian descent, many guidelines consider 18.5–22.9 the lower-risk range.
How accurate is this BMI calculator?
The calculation itself is exact — it uses the standard WHO formula. What varies is how well BMI reflects any one person’s health, for the reasons described in the limitations section above.
Can children use this calculator?
No. Children and teens need BMI-for-age percentiles, because healthy body fat changes as they grow. Ask a paediatrician to plot your child’s BMI on the appropriate growth chart.
What should I do if my BMI is high?
Start with small, sustainable changes to food and activity, and check your daily calorie needs with our TDEE & Calorie Calculator. If your BMI is over 30, or you have any symptoms or conditions, talk to your doctor before starting a weight-loss programme.
Want to go further? Work out your daily calorie target with the TDEE & Calorie Calculator, plan better rest with the Sleep Cycle Calculator, and check your hydration with the Water Intake Calculator.