Muscle and fat weigh the same to BMI
A strong person can read as overweight, and someone who has lost muscle can read as healthy.
Personalized and free
3 minutes
BMI calculator
See your BMI and what it means, the healthy weight range for your height, and a clear plan of calories, protein, carbs and fat to get there, with the date you could reach your goal.
Answer a few quick questions, tell us what you ate, and get your BMI with a plan built around your body.
- Your BMI and healthy weight range
- A weight-loss plan with your macros
- When you could reach your goal
Protein BuddyThe short answer
How to calculate your BMI
BMI, or body mass index, is your weight in kilograms divided by your height in metres squared. In pounds and inches, multiply your weight by 703 and divide by your height in inches squared. For adults, a BMI of 18.5 to 24.9 is a healthy weight. At 5 feet 5 inches that is about 111 to 150 lb.
The formula this calculator uses
- Weigh and measure. Use your weight in kilograms (or pounds) and your height in metres (or inches).
- Apply the formula. BMI = weight (kg) ÷ height (m)². In pounds: BMI = 703 × weight (lb) ÷ height (in)².
- Find your range. Under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, 30 or more obesity.
- Turn it into a weight. Your healthy weight range is 18.5 × height² to 24.9 × height², in kilograms.
BMI ranges for adults
| BMI | Range |
|---|---|
| Under 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 or more | Obesity |
Worked examples
| Height and weight | BMI | Range | Healthy weight |
|---|---|---|---|
| 5′4″, 140 lb (163 cm, 63.5 kg) | 24.0 | Healthy weight | 108 to 145 lb |
| 5′5″, 170 lb (165 cm, 77 kg) | 28.3 | Overweight | 111 to 150 lb |
| 5′7″, 200 lb (170 cm, 91 kg) | 31.3 | Obesity | 118 to 159 lb |
Read it the right way
What BMI can and cannot tell you
BMI is a quick, useful screen. These are the places it needs a second look.
After 40, composition shifts
Muscle tends to fall and fat moves to the middle, often with no change on the scale.
Waist is a second check
NICE suggests keeping your waist under half your height, alongside BMI.
Family background matters
Health risks start at a lower BMI for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background.
The plan matters more than the number
Losing fat while keeping muscle needs the right calories and enough protein. That is why your result comes with a full plan, not only a BMI.
From number to plan
How your plan to a healthy BMI is built
Your daily burn comes from the Mifflin-St Jeor equation and your activity. The plan eats 10 to 20% under it, never below 1,200 kcal for women or 1,500 for men, sets protein first from your body, gives fat about 30% of calories and carbs the rest. See the macro calculator for the full method.
A helpful estimate
BMI is a screening tool, not a diagnosis, and it is not meant for pregnancy, children or teenagers. Food estimates without a photo or grams are approximate. If you are managing a health condition, ask a qualified clinician what weight and pace are right for you.
Check our sources
Research and guidance
Want to check our work? These sources explain the numbers we use.
- World Health OrganizationDefines BMI and the adult ranges.
- NIH National Heart, Lung, and Blood InstituteExplains BMI and its limits.
- NICE on waist-to-height ratioKeep your waist under half your height.
- NICE on BMI and ethnic backgroundLower thresholds for higher-risk groups.
- WHO expert consultation on Asian populationsWhy risk can start at a lower BMI.
- Body composition through menopauseHow muscle and fat change in midlife.
- Mifflin-St Jeor equationThe resting energy equation behind your plan.
- Muscle during weight loss reviewHow much of lost weight is muscle, with and without exercise.
Frequently asked questions
- How do I calculate my BMI?
- Divide your weight in kilograms by your height in metres squared. In pounds and inches, multiply your weight by 703 and divide by your height in inches squared. For example, 170 lb at 5 feet 5 inches is a BMI of about 28.3.
- What is a healthy BMI?
- For adults, the World Health Organization calls 18.5 to 24.9 a healthy weight, 25 to 29.9 overweight and 30 or more obesity. The calculator also turns that range into a weight range for your height.
- Is BMI accurate for women over 40?
- BMI is a quick screen, not a diagnosis. It cannot tell muscle from fat or show where fat sits, and after 40 muscle tends to fall while fat moves to the middle. Keeping your waist under half your height is a useful second check.
- Is BMI different for different ethnic backgrounds?
- Yes. NICE advises lower thresholds, 23 for overweight and 27.5 for obesity, for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, because health risks start at a lower BMI.
- Why does the BMI calculator ask what I ate?
- Knowing your BMI does not tell you what to change. Comparing your day with a plan for your body shows which part is off: calories, protein, carbs or fat. Foods you type in are estimated from a typical portion, so the comparison is approximate.
- How long will it take to reach a healthy BMI?
- The timeline uses your weight-loss calories and about 7,700 kcal per kilogram of body fat, slowing as your weight falls. It is an estimate: real weeks go up and down.
- Is it free?
- The calculator is free and asks for no email. At the end you can get a free gift code for Protein Buddy, so you can track a real day exactly on iPhone or Android.