Lifestyle
Food & Nutrition
FitnessCheck if your weight is in the healthy range for your height.
This tool is for general information only and is not medical advice. Talk to a healthcare professional about results that concern you.
What Is BMI and What Does Your Number Mean?
Body Mass Index (BMI) is a quick screening number that compares your weight to your height. Doctors and health organizations like the CDC and WHO use it as a first check to see whether your weight falls in a range linked to good health. It takes ten seconds to calculate and it works the same whether you use kilograms and centimeters or pounds and feet.
The formula is simple: your weight in kilograms divided by your height in meters squared. In imperial units, it is your weight in pounds times 703, divided by your height in inches squared. Our calculator does the math for you and shows where you land on the scale.
BMI Categories for Adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity class 1 |
| 35.0 to 39.9 | Obesity class 2 |
| 40 and above | Obesity class 3 |
These cutoffs apply to adults aged 20 and older. For children and teens, BMI is compared against growth charts for their age and sex instead of fixed numbers, so this tool is not meant for anyone under 20.
Where BMI Falls Short
BMI cannot tell muscle from fat. A muscular athlete can score as overweight while carrying very little body fat, and an older adult can have a normal BMI while carrying more fat than is healthy. It also says nothing about where you store fat, which matters a lot for health risk. If you want a fuller picture, pair your BMI with our body fat calculator and waist to hip ratio calculator.
BMI Guides for Specific Groups
The BMI formula is the same for everyone, but what a healthy number looks like shifts with sex and age. We have dedicated guides that pair this calculator with the right interpretation for your situation:
- BMI Calculator for Women: body fat differences, cycle effects, and the waist measurement that completes the picture
- BMI Calculator for Men: the muscle problem, the hidden belly fat problem, and the 102 cm waist rule
- BMI for Women Over 50: what menopause does to the number and why 25 to 27 reads differently now
- BMI for Seniors (65+): why research finds the lowest risk at 24 to 30 and when weight loss becomes the red flag
Frequently Asked Questions
What is a healthy BMI?
For most adults, a healthy BMI sits between 18.5 and 24.9. The calculator above also shows the weight range that corresponds to those numbers for your exact height, which is more useful than the BMI number alone.
Is BMI accurate if I lift weights or have a lot of muscle?
Not very. Muscle weighs more than fat, so muscular people often get a BMI in the overweight range even with low body fat. In that case a body fat measurement or waist measurement tells you much more than BMI does.
Is BMI calculated differently for men and women?
No. The formula is identical for both sexes. Women naturally carry a little more body fat than men at the same BMI, which is one more reason BMI is a screening number rather than a diagnosis.
How can I lower my BMI safely?
A steady calorie deficit of 250 to 500 calories a day, more daily movement, and enough protein to protect your muscle is the approach most experts recommend. Aim to lose about 0.25 to 0.5 kg (0.5 to 1 lb) a week. Our calorie calculator gives you a daily target.
Does BMI work during pregnancy?
No. Weight gain in pregnancy is expected and healthy, so BMI categories do not apply. Use our pregnancy weight gain calculator instead, which is based on Institute of Medicine guidelines.
Sources
- Calculate Your BMI | NHLBI, NIH · NIH National Heart, Lung, and Blood Institute
- Obesity and overweight · WHO
- Body mass index: MedlinePlus Medical Encyclopedia · MedlinePlus (NIH)
- Physiology, Body Mass Index – StatPearls – NCBI Bookshelf · NCBI Bookshelf (NIH)
This calculator is for general information only and is not a substitute for professional medical advice, diagnosis, or treatment.
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