How is BMI calculated?

BMI = weight (kg) ÷ height (m)². The standard WHO categories are: below 18.5 Underweight, 18.5–24.9 Healthy weight, 25–29.9 Overweight, 30 and above Obese. BMI is a screening tool and does not diagnose body fatness or health on its own.

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain basic functions. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to estimate how many calories you actually burn each day. This calculator uses the Mifflin-St Jeor equation, which is considered the most accurate for most adults: Male: 10×kg + 6.25×cm − 5×age + 5. Female: 10×kg + 6.25×cm − 5×age − 161.

Is my health data private?

Yes, completely. All calculations happen inside your browser using JavaScript. No data is stored or transmitted anywhere — not even anonymously.

What is a healthy BMI range?

A BMI between 18.5 and 24.9 is classed as healthy weight by the WHO. Below 18.5 is underweight and 25 or above is overweight. For a 175 cm (5 ft 9 in) adult, a healthy weight is roughly 57–76 kg (125–168 lb).

Does BMI work for athletes and muscular people?

Not well. BMI uses only height and weight, so it cannot tell muscle from fat. Very muscular people often score as overweight despite low body fat. For body composition, use the body fat or waist-to-height calculator instead.

Why does the calculator ask for my age and sex if BMI does not use them?

Age and sex are not part of the BMI formula, but they are needed for the BMR and TDEE figures shown alongside it. The Mifflin-St Jeor equation subtracts 5 per year of age and differs by sex (+5 for men, −161 for women).

How many calories should I eat to lose or gain weight?

Start from your TDEE (maintenance). To lose weight, eat below it — a 500 kcal/day deficit yields roughly 0.45 kg (1 lb) of fat loss per week. To gain, eat 300–500 kcal above TDEE. Use the calorie deficit calculator for a precise target.

BMI / BMR / TDEE Calculator

BMI, BMR and TDEE calculator — all three in one place

This tool calculates three core body and nutrition metrics from a single set of inputs: your body mass index (a screening number for weight relative to height), your basal metabolic rate (calories burned at rest) and your total daily energy expenditure (your real maintenance calories). It is built for anyone planning a diet, tracking fitness, or simply checking whether their weight sits in the healthy range. Switch between metric (kg, cm) and imperial (lb, ft/in) at any time.

How it works

BMI ignores age and sex: it is simply weight (kg) ÷ height (m)², with the WHO category bands applied to the result. Imperial inputs are converted first (1 lb = 0.453592 kg, 1 in = 2.54 cm).

BMR uses the Mifflin-St Jeor equation, the most accurate predictive formula for healthy adults:

Male: 10 × kg + 6.25 × cm − 5 × age + 5
Female: 10 × kg + 6.25 × cm − 5 × age − 161

TDEE then multiplies BMR by an activity factor between 1.2 (sedentary) and 1.9 (extra active). All three numbers update instantly and the exact formula used is shown in the results panel.

Example

A 30-year-old man, 175 cm and 75 kg, lightly active:

BMI = 75 ÷ 1.75² = 75 ÷ 3.0625 = 24.5 → Healthy weight
BMR = 10×75 + 6.25×175 − 5×30 + 5 = 750 + 1093.75 − 150 + 5 = 1,699 kcal/day
TDEE = 1,699 × 1.375 = 2,336 kcal/day (maintenance)

BMI	WHO category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 and above	Obese

Activity level	TDEE multiplier
Sedentary (little/no exercise)	1.2
Lightly active (1–3 days/week)	1.375
Moderately active (3–5 days/week)	1.55
Very active (6–7 days/week)	1.725
Extra active (hard exercise + physical job)	1.9

Everything runs entirely in your browser — your age, weight and height are never uploaded anywhere.