Body Mass Index (BMI) is a simple measure using your height and weight to estimate body fat. Enter your details below to see where you fall and what it means for your health.
BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, or fat distribution. Consult a healthcare provider for a complete assessment.
BMI = weight (kg) ÷ height (m)², or in imperial: weight (lb) × 703 ÷ height (in)². A healthy BMI for adults is 18.5 to 24.9; 25-29.9 is overweight; 30 or higher is obese (WHO classification). BMI does not distinguish muscle from fat, so trained or muscular individuals should pair it with body fat %.
Source: World Health Organization · NIH NHLBIBody Mass Index (BMI) is a numeric value calculated from your height and weight that estimates whether your body weight falls within a healthy range for your height. It was first developed in the 1830s by a Belgian mathematician named Adolphe Quetelet, and it's still the most widely used screening tool for weight status today.
Because it only requires two numbers, height and weight, BMI is cheap, fast, and scalable. That's why doctors, insurance companies, public health researchers, and the World Health Organization (WHO) all rely on it. But those same strengths are also its weaknesses: BMI doesn't know whether your weight comes from muscle, fat, bone, or water.
Think of BMI as a starting point for a conversation about your health, not the final word.
BMI is weight divided by height squared. The metric formula is:
BMI = weight (kg) ÷ height² (m²)
In imperial units, the formula adds a conversion factor:
BMI = [weight (lbs) ÷ height² (in²)] × 703
For example, a person who is 5'10" (70 inches) and weighs 180 pounds has a BMI of 25.8, placing them in the overweight category by standard classifications. That's a tidy number, but the person could be an athlete with low body fat, or sedentary with high body fat. The formula can't tell the difference.
Our BMI calculator above handles the math automatically, just input your height and weight.
The World Health Organization (WHO) and the Centers for Disease Control (CDC) use the following BMI categories for adults aged 20 and older:
| BMI Range | Category | What it may indicate |
|---|---|---|
| Below 18.5 | Underweight | Possible undernutrition, hormonal issues, or underlying health concerns |
| 18.5 - 24.9 | Healthy weight | Lower risk of weight-related disease for most adults |
| 25.0 - 29.9 | Overweight | Increased risk of cardiovascular and metabolic conditions |
| 30.0 - 34.9 | Obesity Class I | Significantly elevated disease risk |
| 35.0 - 39.9 | Obesity Class II | High risk of serious health complications |
| 40.0 + | Obesity Class III | Very high risk; often a candidate for medical intervention |
These ranges apply to most adults but not everyone. Children and teens use age- and sex-specific percentile charts instead. Some populations, including people of South Asian descent, have increased cardiometabolic risk at lower BMI thresholds, so public health guidance in those groups often uses slightly lower cutoffs.
At the population level, BMI is one of the strongest predictors of long-term health outcomes. Decades of research show that obesity, BMI 30 and above, is associated with meaningfully higher risk of serious conditions.
Excess body fat, especially around the abdomen, drives insulin resistance. Obesity is the single biggest modifiable risk factor for type 2 diabetes.
Higher BMI correlates with high blood pressure, unfavorable cholesterol profiles, and elevated rates of heart attack and stroke.
The American Cancer Society links obesity to increased risk of at least 13 cancers, including colon, breast (postmenopausal), kidney, liver, and endometrial.
Non-alcoholic fatty liver disease (NAFLD) is strongly tied to obesity and can progress to cirrhosis and liver failure.
Excess tissue around the upper airway raises the risk of obstructive sleep apnea, which damages cardiovascular and cognitive health.
Every extra pound of body weight puts roughly four extra pounds of pressure on the knees. Obesity accelerates osteoarthritis.
Being underweight (BMI under 18.5) also carries real risks, including bone loss, impaired immune function, fertility issues, and micronutrient deficiencies. BMI isn't just about "too much", it's a two-sided measure of nutritional status.
BMI is useful, but it's not the whole picture. Here's where it can mislead:
A lean, muscular athlete and a sedentary person of the same height and weight have identical BMIs, and very different health profiles. Bodybuilders, football players, and gymnasts routinely register as "overweight" or "obese" by BMI despite having single-digit body fat.
Two people can share a BMI of 27 but have wildly different cardiometabolic risk depending on where they carry fat. Visceral fat (around organs) is far more dangerous than subcutaneous fat (under the skin). Waist circumference, above 40 inches for men, above 35 inches for women, is often a better indicator of metabolic risk than BMI alone.
BMI thresholds were developed primarily from data on white Europeans. Research shows people of South Asian descent face elevated cardiometabolic risk at lower BMI, while some Pacific Islander groups have healthier outcomes at higher BMI than the standard chart would suggest. Older adults may also benefit from slightly higher BMI (25-27) for longevity and reduced frailty.
A single BMI reading doesn't capture weight changes over time. A steady gain of 15 pounds over five years tells a different story than the same current weight maintained for a decade.
Better together: Pair BMI with waist circumference, body composition (DEXA scan or bioelectrical impedance), blood pressure, fasting glucose, and a lipid panel. That's how clinicians actually evaluate metabolic health, not a single number in isolation.
If your BMI falls outside the healthy range, the good news is that sustainable changes to nutrition, movement, and sleep can shift it meaningfully over 6-12 months, often with health benefits that begin well before the number itself moves.
Not usually. BMI can't distinguish between muscle and fat, so highly muscular people often register as overweight or obese despite having low body fat. If you're muscular, use body fat percentage (via DEXA, BodPod, or bioelectrical impedance) or waist-to-height ratio instead.
The BMI formula and adult cutoffs are the same regardless of sex. But women naturally carry more body fat at the same BMI than men, so the same BMI often reflects different body composition. For a more sex-specific view, consider body fat percentage: 21-35% is typical for women, 8-24% for men.
For most adults, the standard 18.5-24.9 range applies. But for adults over 65, evidence suggests that a slightly higher BMI (25-27) is associated with lower mortality and reduced frailty. Preserving muscle mass matters more than chasing a specific BMI number later in life.
Not the same way. Children and teens use BMI-for-age percentiles that compare their BMI to others of the same age and sex. Categories are underweight (below 5th percentile), healthy (5th-85th), overweight (85th-95th), and obese (95th and above).
Safely, about 1-2 points per 8-12 weeks with consistent lifestyle changes. A typical sustainable weight loss of 1-2 pounds per week moves BMI by roughly 0.15-0.30 per week. Faster changes are usually water weight or muscle loss, not fat, and rarely stick.
No. BMI treats all body types the same. Some people naturally have larger frames, denser bones, or a higher muscle baseline. Waist circumference, waist-to-hip ratio, and body fat percentage give a more complete picture.
BMI is a proxy for body fat based on height and weight. Body fat percentage is a direct measure of how much of your body weight is fat. Body fat percentage is more accurate but requires specialized measurement (DEXA, BodPod, bioelectrical impedance, or skinfold calipers).
At a population level, yes, there's a clear U-shaped curve. Mortality rises modestly at BMI below 20 and steeply at BMI above 30. But individual risk depends on body composition, fitness, metabolic markers, and lifestyle. A fit person with BMI 27 often has lower mortality risk than an unfit person with BMI 22.
BMI is a fast screen but a blunt one. These tools refine the number into something actually useful, body composition, calorie needs, and the hormones underneath.
Hand-picked guides from our physician-edited library on weight loss, body composition, metabolism, and the hormonal levers behind them.
SURMOUNT-1 studied FDA-approved branded tirzepatide (Zepbound® 15 mg weekly) over 72 weeks — the largest GLP-1 weight-loss trial to date. Compounded preparations are not FDA-approved. If your BMI is 27+ with a comorbidity (sleep apnea, hypertension, prediabetes) or 30+, you likely qualify for prescribed GLP-1 therapy through OPTML.
How this tool calculates
BMI = weight (kg) / height² (m²), the World Health Organization standard formula. We use the WHO classification: under 18.5 = underweight; 18.5-24.9 = normal; 25.0-29.9 = overweight; ≥30.0 = obese.
Peer-reviewed sources
Important. This tool is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment. The tool does not prescribe medication, recommend specific dosing, or substitute for clinical evaluation. Compounded medications referenced anywhere on this site are not FDA-approved; the FDA does not verify the safety, effectiveness, or quality of compounded drugs. Treatment decisions are made only by a licensed U.S. physician after individual patient evaluation.