BMI stands for Body Mass Index. It is a number calculated from your height and weight using this formula: BMI = Weight (kg) ÷ Height (m)². For example, if you weigh 70 kg and are 1.75 m tall, your BMI is 70 ÷ (1.75 × 1.75) = 22.9. Our free BMI calculator does this calculation instantly for you in both metric and imperial units.

According to the World Health Organization (WHO), a healthy BMI for adults is between 18.5 and 24.9. Below 18.5 is considered underweight, 25 to 29.9 is overweight, and 30 or above is obese. For South Asian and East Asian populations, health risks can appear at a lower BMI — overweight is often defined as BMI above 23 for these groups.

BMI is a useful screening tool but it has limitations. It does not distinguish between muscle and fat — so a very muscular person may show a high BMI despite having low body fat. It also does not account for age, gender differences in fat distribution, or where fat is stored in the body. For a more complete picture, use BMI alongside our Body Fat % Calculator and waist circumference measurements.

If you are actively trying to lose or gain weight, recalculating your BMI every 4 weeks is a good way to track progress. For general health monitoring once every 3 to 6 months is sufficient. Remember that BMI changes slowly — daily fluctuations in weight from water, food, and other factors mean short-term BMI changes are not meaningful.

Our BMI calculator is designed for adults aged 18 and above. For children and teenagers, BMI is interpreted differently using age and gender specific growth charts — a process called BMI-for-age. If you want to assess a child’s BMI, please consult their paediatrician who can use the appropriate charts for their age and gender.

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — just to keep you alive (breathing, heartbeat, organ function). TDEE (Total Daily Energy Expenditure) is your BMR multiplied by your activity level — it represents the total calories you burn in a day including exercise and movement. TDEE is the number you should use for planning your diet.

To lose weight safely you need to eat fewer calories than you burn — creating a calorie deficit. A deficit of 500 calories per day typically results in approximately 0.5 kg (1 lb) of weight loss per week, which is a safe and sustainable rate. Our TDEE calculator automatically calculates your weight loss calorie target when you select the “Lose weight” goal. Avoid going below 1,200 calories per day for women or 1,500 for men without medical supervision.

Our calorie calculator uses the Mifflin-St Jeor equation — the most widely validated formula for estimating calorie needs, recommended by dietitians worldwide. Research shows it is accurate within 10% for most people. However individual metabolism varies, so treat the result as a starting point. If you are not seeing the results you expect after 2 to 3 weeks, adjust your intake by 100 to 200 calories and monitor progress.

Macros (macronutrients) are the three main nutrients in food: protein, carbohydrates, and fats. Each provides calories — protein and carbs give 4 calories per gram, fat gives 9 calories per gram. Our TDEE calculator automatically calculates your recommended macro breakdown alongside your calorie target. Hitting your macros — not just your total calories — helps optimise body composition, energy levels, and performance.

Healthy body fat percentages differ between men and women. For men: essential fat is 2–5%, athlete range is 6–13%, fitness range is 14–17%, acceptable is 18–24%, and obese is 25% or above. For women: essential fat is 10–13%, athlete range is 14–20%, fitness range is 21–24%, acceptable is 25–31%, and obese is 32% or above. Women naturally carry more body fat than men due to hormonal differences.

Our body fat calculator uses the US Navy circumference method — a widely used and validated formula developed by the United States Navy. It estimates body fat percentage using measurements of height, waist, neck, and hip (for women). While not as precise as DEXA scanning or hydrostatic weighing, it provides a reliable estimate without any special equipment.

For the most accurate results: Waist — measure at the narrowest point of your waist, typically just above your belly button. Stand relaxed, do not suck in. Neck — measure just below the larynx (Adam’s apple), with the tape slightly sloped downward at the front. Hip (women only) — measure at the widest point of your hips and buttocks. Use a flexible measuring tape and take measurements in the morning before eating for consistency.

Yes — all calculators on Body Calc Tools are completely free to use with no registration, no subscription, and no hidden fees. We keep the site free through advertising and affiliate links to products we genuinely recommend.

Yes! All our calculators support both metric (kg, cm) and imperial (lbs, feet and inches) units. Simply click the Metric or Imperial toggle button at the top of any calculator to switch between units. The calculator will automatically convert and compute your results in the selected unit system.

No. All calculations on Body Calc Tools happen entirely in your browser. We do not store, collect, or transmit any of the personal data you enter into our calculators (weight, height, age, measurements). The only data we collect is standard anonymous website analytics (pages visited, country, browser type) through Google Analytics. Please see our Privacy Policy for full details.

No. All results from our calculators are for informational and educational purposes only. They are estimates based on scientifically validated formulas and should not be used as a substitute for professional medical or nutritional advice. Always consult a qualified healthcare professional before making significant changes to your diet, exercise routine, or health plan.

You can reach us through our Contact page. We typically respond within 24 to 48 hours. We welcome feedback, suggestions for new calculators, and any questions you may have about our tools.

We currently offer five free fitness calculators: BMI Calculator (Body Mass Index), Calorie/TDEE Calculator (daily calorie and macro targets), Body Fat % Calculator (using the US Navy method), Ideal Weight Calculator (based on height and frame size), and BMR Calculator (Basal Metabolic Rate). All support both metric and imperial units and provide personalised advice with your results.