Free BMI Calculator

Check your Body Mass Index instantly — metric or imperial, with your healthy weight range and visual result.

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BMI Categories WHO Standard 18.5 25 30 Under Normal Over Obese ＜18.5 Under weight 18.5–24.9 Normal weight 25–29.9 Over weight 30+ Obese Source: World Health Organization (WHO) Health risk lowest risk in normal range

What Is a Healthy BMI? Understanding the Ranges

Body Mass Index (BMI) is a screening tool that estimates body composition based on height and weight. Developed from population studies and endorsed by the World Health Organization (WHO) and CDC, it remains one of the most widely used starting points for weight health assessment.

For most adults aged 18-65, the healthy BMI range is 18.5 to 24.9. This range is associated with the lowest risk for cardiovascular disease, type 2 diabetes, and other weight-related conditions.

Category BMI Range Risk Level
Underweight Below 18.5 Moderate
Normal weight 18.5 – 24.9 Lowest
Overweight 25.0 – 29.9 Elevated
Obese 30.0 and above High

BMI is a screening tool, not a diagnostic measure. Always consult a healthcare provider for a full health assessment.

Further reading: What Is a Healthy BMI Range? A Complete Guide →

The BMI Formula
Metric
BMI = weight (kg) ÷ height² (m)
e.g. 70 kg ÷ (1.75 * 1.75) = 22.9
Imperial
BMI = (lbs ÷ inches²) * 703
e.g. (154 ÷ 71²) * 703 = 21.5
Formula standardized by the National Institutes of Health (NIH)

How Is BMI Calculated? The Formula Explained

BMI divides your weight by the square of your height. The resulting number places you in one of four standard categories established by the WHO and NIH.

In metric units, you divide kilograms by metres squared. In imperial units, the same ratio is multiplied by 703 to convert from inches to metres. Both formulas give the same result.

Our calculator handles both unit systems automatically — just enter your numbers and click Calculate.

For people of South Asian, East Asian, Black African, or Middle Eastern descent: Research shows health risks — including type 2 diabetes and cardiovascular disease — begin at a lower BMI, around 23. The NHS and WHO both recognise this adjusted threshold. Our results display the standard ranges but this is important context for your reading.

References: WHO Obesity Fact Sheet · CDC BMI About

BMI Limitations by Group Athletes BMI may show overweight due to high muscle mass Use: Body fat % test Seniors 65+ BMI 25–27 is often healthier — protects against falls & illness Consult: GP for advice Women Naturally carry more body fat than men at the same BMI Also: not for pregnancy South/East Asian Health risks start at BMI 23, not 25 (WHO adjusted threshold)

BMI by Gender, Age & Ethnicity — Key Differences

BMI uses the same formula for everyone, but its interpretation changes significantly depending on who's using it. Understanding these differences helps you read your result more accurately.

  • Men vs. women: Women naturally carry 5–10% more body fat than men at the same BMI. A woman at BMI 25 typically has a higher body fat percentage than a man at BMI 25.
  • Seniors (65+): Research suggests a BMI of 25–27 may actually be protective for older adults, offering a buffer against frailty, bone density loss, and illness recovery.
  • Athletes: High muscle mass can push BMI into the overweight or obese range even with low body fat. BMI is not a reliable indicator for highly trained athletes.
  • South Asian, East Asian, Black African, and Middle Eastern populations: Higher cardiometabolic risk at lower BMI — the WHO recommends considering overweight at BMI 23 and obese at 27.5 for these groups.
  • Children and teens: Standard adult BMI does not apply. Use a BMI-for-age percentile chart from the CDC for anyone under 18.

How to Reach a Healthy BMI

If your result is outside the normal range, these science-backed strategies can help you move in the right direction.

Track what you eat
Logging food for even one week builds awareness of calorie patterns. You don't need to count forever — just identify habits.
Aim for 1–2 lbs per week
Slow, steady weight loss is far more sustainable than crash diets. A 500 kcal daily deficit is a good target — equivalent to one less meal or one extra 45-min walk.
Protein at every meal
Protein keeps you full longer than carbohydrates or fat. Eggs, legumes, Greek yogurt, and lean meat all reduce overall calorie intake naturally.
8,000+ steps daily
Walking burns 300–400 extra calories a day with near-zero injury risk. It also reduces cortisol — a hormone that promotes abdominal fat storage.
Prioritise sleep
Under 7 hours per night raises ghrelin (hunger hormone) and cortisol, making weight management significantly harder. Sleep is an underrated tool.
Strength train 2× weekly
Muscle tissue burns more calories at rest than fat. Two sessions a week of resistance training measurably improves body composition and BMI long-term.

Frequently Asked Questions About BMI

Honest, evidence-based answers to the most common BMI questions.

BMI = weight in kilograms divided by the square of your height in metres. In imperial units: (weight in lbs ÷ height in inches²) × 703. For example, a person weighing 70 kg at 1.75 m has BMI = 70 ÷ (1.75²) = 22.9 — in the normal range.
Not reliably. Athletes with significant muscle mass can have a BMI in the overweight or obese category while having very low body fat. Muscle is denser and heavier than fat, so BMI overstates fatness in muscular people. Body fat percentage testing — via DEXA scan, skinfold calipers, or bioelectrical impedance — gives a more accurate picture for athletes.
A BMI below 18.5 is classified as underweight by the WHO. This can indicate insufficient calorie or nutrient intake, or an underlying medical condition. If you are underweight, calorie-dense whole foods (nuts, avocados, legumes, dairy, protein-rich meals) can help you gain weight sustainably. Consult a GP if you have been losing weight unintentionally.
Yes — this is known as normal weight obesity, or metabolically obese normal weight (MONW). BMI measures overall body weight relative to height, but cannot detect where fat is stored. Visceral fat (fat around the organs) is the most metabolically dangerous type. Waist circumference is a better proxy: above 88 cm (35 in) for women or 102 cm (40 in) for men indicates elevated risk regardless of BMI.
Monthly or quarterly is usually enough to track meaningful trends. Checking daily is not recommended — normal fluctuations in water retention, digestion, and food timing can cause weight to vary by 1–3 kg in a single day, making readings misleading. Focus on the direction of change over weeks rather than absolute numbers day-to-day.
Standard adult BMI ranges do not apply to children and teenagers because body fat norms change significantly as children grow. For anyone aged 2–19, the CDC recommends using a BMI-for-age percentile chart, which compares a child's BMI against others of the same age and sex. Our calculator is intended for adults aged 18 and over.
How we keep this accurate: BMI categories and thresholds on this page follow standards set by the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and the National Heart, Lung, and Blood Institute (NHLBI). This page was last reviewed April 2026. This tool is for informational purposes only and is not a substitute for professional medical advice — please consult a healthcare provider for personalised guidance. About CalcMeter →