BMI, BMR and TDEE Explained: How Many Calories You Need

By MavexTech · Updated 16 October 2026 · 9 min read

BMI tells you whether your weight is in a healthy range for your height, BMR is the calories your body burns at complete rest, and TDEE is BMR multiplied by your activity level: your real daily calorie burn. To maintain weight, eat about your TDEE; to lose about 0.45 kg a week, eat roughly 500 kcal below it, without going much under your BMR.

Three numbers, three different questions

BMI, BMR and TDEE are often mentioned together, but they answer different questions:

• BMI (Body Mass Index) asks: is my weight in a healthy range for my height? It is a screening number, not a measure of body fat.
• BMR (Basal Metabolic Rate) asks: how many calories does my body burn at complete rest, just to keep me alive (breathing, heartbeat, brain, body temperature)?
• TDEE (Total Daily Energy Expenditure) asks: how many calories do I burn in a full day, including work, walking and exercise? This is the number that decides whether you gain, lose or maintain weight.

The practical order is: check BMI to see whether weight change is worth aiming for, calculate BMR, multiply it by an activity factor to get TDEE, then set a calorie target above or below TDEE.

BMI: formula, categories and Indian cut-offs

Example A: a man who is 175 cm tall and weighs 80 kg has a BMI of 80 / (1.75 × 1.75) = 80 / 3.0625 = 26.12.

Example B: a woman who is 160 cm tall and weighs 60 kg has a BMI of 60 / (1.6 × 1.6) = 60 / 2.56 = 23.44.

Which categories should Indians use?

The World Health Organization categories are used worldwide. Research shows that South Asians tend to carry more body fat and face higher risk of diabetes and heart disease at a lower BMI, so Indian consensus guidelines (2009) use lower cut-offs for adults:

This changes the answer for Example B: a BMI of 23.44 is “normal” on the WHO scale but “overweight” on the Indian cut-offs. Example A’s 26.12 is overweight by WHO and obese by the Indian scale.

Healthy weight range for your height

Rearranging the formula gives a weight range: weight = BMI × height². For two common heights:

Where BMI goes wrong

• Muscular people can show a high BMI with low body fat.
• Older adults may lose muscle and show a “normal” BMI despite high body fat.
• Children and teenagers need age- and sex-specific BMI charts, not adult categories.
• Pregnancy makes BMI unsuitable as a guide.

Waist size adds useful information. A waist-to-hip ratio or body fat estimate helps when BMI and appearance do not match.

BMR: the calories you burn at rest

BMR cannot be measured at home precisely, so it is estimated with equations. The most widely recommended for adults is Mifflin-St Jeor (1990), which is also what the MavexTech BMR and TDEE calculators use:

Example A (man, 30 years, 175 cm, 80 kg): 800 + 1,093.75 − 150 + 5 = 1,748.75 kcal/day, about 1,749.

Example B (woman, 28 years, 160 cm, 60 kg): 600 + 1,000 − 140 − 161 = 1,299 kcal/day.

Other BMR formulas

• Revised Harris-Benedict (1984): for Example A it gives about 1,830 kcal, and for Example B about 1,377 kcal, around 5% to 6% higher than Mifflin-St Jeor in these two cases.
• Katch-McArdle: BMR = 370 + 21.6 × lean body mass (kg). It needs your body fat percentage. If Example A has 25% body fat, lean mass is 60 kg and BMR = 370 + 21.6 × 60 = 1,666 kcal.

Different equations giving answers 100 to 150 kcal apart is normal. Any formula is an estimate, and individual BMR can differ by around 10% either way, so treat the result as a starting point and adjust with real-world results.

TDEE: your real daily calorie burn

TDEE adds everything you do on top of BMR: digesting food, daily movement, and exercise. The standard way to estimate it is to multiply BMR by an activity factor:

Values are rounded to the nearest calorie. Most people overestimate their activity. If you sit at a desk all day and go to the gym three times a week, “lightly active” is usually closer to the truth than “moderately active”. Daily steps matter as much as workouts; a job that keeps you on your feet can add more than an hour of exercise.

Turning TDEE into a calorie target

Your TDEE is your maintenance calories: eat about this much and your weight should stay roughly stable. To change weight, eat a little less or a little more.

A common rule of thumb is that 1 kg of body fat stores about 7,700 kcal. A daily deficit of 500 kcal adds up to 3,500 kcal a week, which suggests roughly 3,500 / 7,700 = 0.45 kg of fat loss per week. Real results vary because water, muscle and metabolism also shift, and weight loss usually slows over time.

Using Example A (moderately active, TDEE 2,711) and Example B (lightly active, TDEE 1,786):

Note on Example B: a 500 kcal deficit would put her at 1,286 kcal, just below her BMR of 1,299. Very low intakes are hard to sustain and can make it difficult to get enough protein, iron and other nutrients. A smaller deficit of 250 to 300 kcal, combined with more daily walking to raise TDEE, is the more sensible route for smaller, lightly active people. Anyone planning to eat below about 1,200 kcal a day should do so only with medical supervision.

Protein and food quality

Calories decide the direction of weight change; protein and food quality decide how you feel and whether you keep muscle. In a typical Indian diet heavy on rice, roti and sugar in tea, the easiest calorie savings often come from portion sizes, fried snacks, sweets and sugary drinks, while adding dal, paneer, curd, eggs, pulses or lean meat helps protein. A macro calculator can split your calorie target into protein, carbohydrates and fat.

Common mistakes when using these numbers

• Eating at BMR instead of TDEE. BMR is the calorie burn at rest. Eating only your BMR is already a large deficit for most people.
• Picking a high activity level. Choose the level that matches your average week, not your best week.
• Counting exercise calories twice. If your activity factor already includes your gym sessions, do not add workout calories on top.
• Judging progress day by day. Body weight swings with water and salt. Compare weekly averages over two to four weeks, then adjust intake by 100 to 200 kcal if needed.
• Ignoring the Asian BMI cut-offs. An Indian adult with a BMI of 23 to 24.9 is already in the overweight range under Indian guidelines.
• Forgetting to recalculate. BMR falls as you lose weight and with age, so recalculate after every 4 to 5 kg of change.

Frequently asked questions

This guide is general information, not medical advice. Calorie needs vary between individuals; consult a doctor or registered dietitian before major diet changes, especially if you are pregnant, have a medical condition or take medication.