Calculate your body mass index (BMI) to see if you're at a healthy weight for your height. BMI is a quick screening tool used by healthcare professionals to assess weight status and potential health risks.
Use this table to understand what your BMI number means and the associated health risk levels.
| Category | BMI Range | Health Implications |
|---|---|---|
| Underweight | Below 18.5 | Increased risk of malnutrition, weakened immunity, osteoporosis |
| Normal Weight | 18.5 - 24.9 | Lowest health risk, optimal for most people |
| Overweight | 25.0 - 29.9 | Increased risk of heart disease, diabetes, high blood pressure |
| Obese Class I | 30.0 - 34.9 | High risk of chronic diseases; lifestyle changes recommended |
| Obese Class II | 35.0 - 39.9 | Very high risk; medical intervention often needed |
| Obese Class III | 40.0 and above | Extremely high risk; comprehensive medical treatment recommended |
Pick Imperial (pounds/feet) or Metric (kg/cm) - whichever you're most comfortable with. You can switch between them anytime.
For weight, use a scale for accuracy. The most consistent reading comes first thing in the morning after using the bathroom. For height, measure without shoes. Stand straight against a wall and have someone mark where the top of your head touches - this gives you a more accurate measurement than estimating from memory.
Age and gender are optional. They provide additional context for your results but don't change the core calculation.
After you calculate, you'll see your score, weight category, and healthy weight range for your height. Think of it as one data point among many. Healthcare providers consider this alongside blood pressure, cholesterol, fitness level, and overall health when making wellness assessments.
Body Mass Index divides your weight by your height squared (weight in kg ÷ height in m²). A Belgian statistician named Adolphe Quetelet created this formula in the 1830s for studying populations, not individuals. The formula was designed for analyzing groups rather than assessing whether any single person is healthy. Healthcare providers use it as a quick screening metric because it's simple and requires no special equipment.
Below 18.5 (Underweight): Signals potential malnutrition, eating disorders, or medical issues. Low weight brings its own risks - weakened immunity, brittle bones, anemia, fertility problems.
18.5-24.9 (Normal): This range shows the lowest disease risk for most people. However, fitness and body composition matter more than just achieving a target number.
25-29.9 (Overweight): Risk increases for heart disease, diabetes, high blood pressure. However, plenty of muscular, active people fall here and they're perfectly healthy. Where you carry fat matters more than the score itself.
30+ (Obese): Significant risk for heart disease, stroke, diabetes, certain cancers, sleep apnea. Risk climbs as the number climbs. Obesity divides into Class I (30-34.9), Class II (35-39.9), and Class III (40+), with health concerns escalating at each level.
Muscle vs Fat: The formula can't distinguish between them. Bodybuilders often score as "obese" despite having 6-10% body fat.
Fat Distribution: Belly fat (visceral fat) that surrounds your organs causes more health problems than hip or thigh fat. Same score can mean very different risk levels depending on where you carry weight.
Age Differences: Older adults lose muscle naturally. Someone over 65 might be healthier at 25-27 than at 22. Children and teens need completely different charts based on growth patterns.
Ethnicity: Asian populations face health risks at lower numbers. WHO uses different thresholds - overweight starts at 23 instead of 25, obese at 27.5 instead of 30. Body composition varies across ethnic groups.
Fitness Level: An active person with a score of 28 may be healthier than a sedentary person at 22. The calculation doesn't capture cardiorespiratory fitness, which has a stronger connection to longevity.
Athletes, bodybuilders, and anyone with above-average muscle mass will get misleading results. NFL running backs average 30 (technically obese) but carry minimal body fat. Same goes for rugby players, gymnasts, powerlifters.
Pregnant women shouldn't use standard ranges. Neither should people recovering from illness or surgery.
Monitor your measurements quarterly or annually. One reading means little - the pattern over time tells the real story.
Waist circumference matters more than your score. Over 40 inches for men or 35 inches for women? That's high risk territory regardless of what the calculator says. Belly fat actively harms your health.
Get blood work done. Cholesterol, blood pressure, blood sugar, inflammation markers - these reveal much more about your actual health than any single body measurement.
Losing 5-10% of your body weight improves health markers significantly. You don't need to reach "normal" to see benefits.
Very fit? Consider body composition testing - DEXA scans or bioelectrical impedance show fat vs muscle. Someone lifting weights regularly might not see their number budge despite getting leaner and stronger. That's normal.
Being "skinny fat" is a thing. Normal score, high body fat percentage, low muscle. Not healthy. Fitness beats thinness every time.
Your score gives you one data point. Here are more accurate ways to assess your health:
Maintaining a healthy weight means maintaining fitness and nutrition habits, not just achieving a number. Get annual checkups for blood pressure, cholesterol, blood sugar. Being thin but sedentary is worse than being slightly heavy but active - focus on overall fitness.
See your doctor to rule out thyroid issues, diabetes, eating disorders, celiac disease, or malabsorption problems. Eat more nutrient-dense foods like nuts, avocados, whole grains, lean proteins, and full-fat dairy. Add strength training to build muscle, not just fat. Low weight brings risks including brittle bones, weak immunity, fertility problems, and slow healing.
Small steps work effectively. Losing 5-10% of your weight improves health markers even if you stay in the overweight range. Focus on diet first - you can't outrun a bad diet. Add 30 minutes of daily walking and get blood work to catch prediabetes, high cholesterol, or blood pressure problems early.
Schedule a complete health assessment with your doctor. Get blood work, blood pressure checked, and heart evaluation. Aim for 1-2 lbs per week - gradual progress lasts longer than crash diets. Consider working with a registered dietitian for personalized meal planning and behavior strategies. Joining a weight loss program or support group can significantly improve your success rate.
For some people, medication (GLP-1 agonists) or bariatric surgery makes sense as part of a comprehensive treatment plan. Discuss all options with your doctor.
Move 150 minutes per week. Eat mostly whole foods. Sleep 7-9 hours. Manage stress.
Health improvements show up in your bloodwork before the scale budges. Don't chase a number - build healthy habits and let your body follow.
BMI provides a useful estimate of weight status but has limitations. Works fine for average people but fails for athletes and muscular folks who score as "overweight" despite being lean and fit. The formula can't tell muscle from fat. For a real health assessment, combine this with waist measurement, body fat percentage, and blood tests. Your cholesterol, blood pressure, and blood sugar provide much better indicators of health than any single number on a scale.
18.5-24.9 works for most adults. Older adults (65+) might be healthier slightly higher at 25-27 because they've lost muscle naturally. Kids and teens need age-specific charts - adult ranges don't apply to growing bodies.
Body composition varies by ethnicity. Asians carry more body fat and visceral fat at the same measurement, developing diabetes and heart disease at lower levels. WHO sets overweight at 23 (not 25) and obese at 27.5 (not 30) for Asian populations.
Yes. This is called "normal weight obesity" or having a "skinny fat" body composition. You might have a normal weight with high body fat percentage and low muscle mass. About 30% of people with normal scores have metabolic problems - high cholesterol, blood pressure issues, or insulin resistance. Your body composition and fitness level provide a more complete picture than weight alone.
Not necessarily. "Metabolically healthy obesity" exists - some people carry extra weight without experiencing negative health consequences. If you're active, eat well, and your blood markers look good (cholesterol, blood pressure, blood sugar), you might be fine. Check your waist measurement too. Under 40 inches for men or 35 for women generally indicates lower risk. Get annual blood work to confirm your metabolic health rather than focusing solely on reaching a specific number.
Aim for 1-2 pounds per week, as gradual weight loss is more sustainable. Faster weight loss sounds tempting but often leads to muscle loss and weight regain. Create a 500-750 calorie daily deficit through diet and activity. Focus on behavior changes you can maintain long-term - eating more vegetables, reducing processed foods, and adding daily movement. Even 5-10% weight loss can significantly improve your health markers.
Muscle is denser, so yes - it weighs more per unit of volume. A pound of muscle takes up 20% less space than a pound of fat. This is why you might not lose pounds when you start lifting weights, even though you're getting leaner and your clothes fit better.