BMI Calculator

Understand Your Body Mass Index and Health

Imagine standing on the scale after months of effort, seeing a number, but having no idea if you're at a healthy weight for your height. You know you're 5'8" and weigh 165 pounds, but is that good, bad, or somewhere in between? Should you lose weight, gain weight, or stay where you are? Your doctor mentions something about BMI during checkups, but you never quite understand what the number means or how concerned you should be. Or you're starting a fitness journey and want to set a realistic goal weight, but without understanding your current BMI and healthy target range, you're essentially guessing where to aim.

Our BMI Calculator transforms raw numbers into meaningful health insights. Enter your height and weight in whatever units are comfortable—feet and pounds, or meters and kilograms—and instantly see your BMI score with a clear explanation of what it means (underweight, normal, overweight, or obese). Get your personalized healthy weight range so you know exactly what weight range is medically recommended for your height. Track your BMI over time with interactive charts showing your progress on weight loss or gain journeys. Set specific weight goals and see how long it will take to reach them at different rates of change. Get health risk assessments and personalized recommendations based on your current BMI category. Export detailed PDF reports to share with your doctor or keep for your records. Whether you're monitoring health, planning fitness goals, or simply curious about your numbers, this calculator gives you the knowledge and tools to make informed decisions about your weight and wellness. No medical jargon, no confusion—just clear, actionable information about your body and health.

Advanced BMI Calculator Features

Understanding BMI Categories and Ranges

BMI (Body Mass Index) is a screening tool that uses your weight and height to estimate body fat and assess health risks. Here's what the numbers mean:

Adult BMI Categories (18+)

How BMI is Calculated

Metric Formula: BMI = weight (kg) ÷ height (m)²

Example: Weight 70 kg, Height 1.75 m → BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86

Imperial Formula: BMI = (weight (lbs) ÷ height (inches)²) × 703

Example: Weight 154 lbs, Height 69 inches → BMI = (154 ÷ (69 × 69)) × 703 = (154 ÷ 4,761) × 703 = 22.74

BMI Limitations and Considerations

• Doesn't Measure Body Fat: BMI uses weight and height, not actual fat percentage. Muscle weighs more than fat, so athletes often have "high" BMI despite low body fat.
• Doesn't Account for Distribution: Where you carry weight matters. Abdominal fat (apple shape) is riskier than hip/thigh fat (pear shape). Waist-to-height ratio provides additional insight.
• Age and Sex Variations: Older adults naturally lose muscle mass. Women typically have higher body fat percentages than men at the same BMI. BMI doesn't adjust for these differences.
• Ethnicity Considerations: Some populations have different health risk thresholds. Asian populations may have higher health risks at lower BMIs. Pacific Islanders may be healthy at higher BMIs.
• Not for Children: Growing children need age and sex-specific BMI percentiles, not adult categories. Our calculator includes pediatric BMI assessment for ages 2-19.

Who Benefits from BMI Tracking

Healthy Weight Ranges by Height

These tables show the weight ranges corresponding to healthy BMI (18.5-24.9) for different heights:

Imperial Units (Feet/Inches & Pounds)

Metric Units (Centimeters & Kilograms)

Healthy Weight Change Guidelines

Safe Weight Loss Rates

Calories and Weight Change

Understanding the relationship between calories and weight:

• 1 pound of body weight = 3,500 calories: To lose 1 pound, create a 3,500 calorie deficit over time. To gain 1 pound, create a 3,500 calorie surplus.
• Daily deficit for 1 lb/week: 3,500 calories ÷ 7 days = 500 calories/day deficit (eat less and/or exercise more)
• Combine diet and exercise: Easier to achieve 500-calorie deficit by eating 300 fewer calories AND burning 200 through exercise than diet alone
• Don't go too low: Women should not go below 1,200 calories/day, men not below 1,500 calories/day without medical supervision
• Weight loss plateaus: As you lose weight, your body requires fewer calories, so you may need to adjust intake or activity to continue losing

Healthy Weight Gain

For those who need to gain weight (underweight BMI):

• Target rate: 0.5-1 pound per week for healthy, gradual weight gain
• Calorie surplus: Add 250-500 calories/day above maintenance needs
• Focus on nutrient-dense foods: Nuts, nut butters, avocados, whole grains, lean proteins, healthy oils—not junk food
• Strength training: Build muscle mass, not just fat, through resistance exercise
• Frequent meals: Eat 5-6 smaller meals throughout the day rather than forcing large meals
• Medical consultation: Unintentional weight loss or difficulty gaining may indicate underlying health issues

Common BMI Questions Answered

Why is my BMI high even though I'm fit?

Answer: BMI doesn't distinguish between muscle and fat. If you have high muscle mass from weight training or athletics, your BMI may categorize you as "overweight" even though you have low body fat. This is a known limitation of BMI. For muscular individuals, body fat percentage and waist-to-height ratio are better indicators. If you're physically fit with a high BMI, you're likely healthy—consult your doctor if concerned.

My BMI is normal, but I have belly fat. Am I healthy?

Answer: Even with normal BMI, excess abdominal fat increases health risks. Measure your waist circumference and calculate waist-to-height ratio (our calculator includes this). For health, waist circumference should be less than half your height. Example: If you're 70 inches tall, your waist should be under 35 inches. "Normal weight obesity" (normal BMI but high body fat percentage) is a real phenomenon. Focus on body composition, not just BMI.

How quickly can I change my BMI?

Answer: BMI changes as you lose or gain weight. Safe weight loss is 1-2 pounds per week. For someone 5'8" tall, losing 1 pound per week decreases BMI by about 0.15 points. To move from BMI 28 (overweight) to BMI 24.9 (normal)—about 20 pounds for this height—would take 10-20 weeks at healthy rates. Rapid BMI changes indicate too-fast weight loss/gain and aren't sustainable or healthy.

Does BMI change with age?

Answer: The BMI formula doesn't change with age, but your body composition does. Older adults naturally lose muscle mass and bone density, which can lower weight and BMI even as body fat percentage increases. Some researchers suggest slightly higher healthy BMI ranges for older adults (65+) may be protective. However, standard BMI categories (18.5-24.9) are still generally used for all adults. Focus on maintaining muscle mass through resistance exercise as you age.

Can I trust online BMI calculators?

Answer: Yes, if they use the correct formula. BMI calculation is straightforward math (weight ÷ height²), so any calculator using the standard WHO formula gives the same result. Our calculator uses the exact WHO-approved formula with proper unit conversions. The calculation is accurate; the interpretation and limitations (doesn't measure body fat, doesn't account for muscle mass, etc.) are what you need to understand. Always verify you're entering measurements in the correct units.

Other Health Measurements Beyond BMI

While BMI is useful, these additional measurements provide a more complete health picture:

Waist Circumference

• What it measures: Abdominal fat, which is metabolically active and increases disease risk
• How to measure: Wrap measuring tape around bare abdomen at navel level, breathe normally, measure without pulling tape too tight
• Healthy ranges: Men under 40 inches (102 cm), Women under 35 inches (88 cm)
• Why it matters: Predicts cardiovascular disease risk independently of BMI

Waist-to-Height Ratio (Our calculator includes this)

• Formula: Waist circumference ÷ Height (both in same units)
• Healthy target: Keep ratio under 0.5 (waist less than half your height)
• Example: 5'8" person (68 inches) should have waist under 34 inches (34 ÷ 68 = 0.5)
• Advantage over BMI: Accounts for fat distribution, not just total weight

Body Fat Percentage

• What it measures: Proportion of your weight that's fat vs. lean mass (muscle, bone, organs)
• Healthy ranges: Men 10-20%, Women 18-28% (athletes lower, older adults slightly higher)
• Measurement methods: Skinfold calipers, bioelectrical impedance scales, DEXA scan (most accurate)
• Why it's better than BMI: Distinguishes between fat and muscle, more accurate for fitness assessment

Other Health Markers

• Blood Pressure: Should be below 120/80 mmHg for optimal health
• Blood Sugar (Fasting): Under 100 mg/dL is normal, 100-125 is prediabetes, 126+ is diabetes
• Cholesterol: Total cholesterol under 200 mg/dL, HDL ("good") over 40 for men / 50 for women
• Resting Heart Rate: 60-100 bpm is normal, lower often indicates better cardiovascular fitness