How to Calculate BMR: The Mifflin-St Jeor Formula, TDEE and Calorie Targets

Every calorie target you have ever been given — 2,000 a day, a deficit you found on a forum, an app default — is a guess about one number: how much energy your body actually burns. That number has a name, a formula and a worked example, and none of it requires a lab. This guide explains how to calculate your BMR with the Mifflin-St Jeor equation, how to turn it into a TDEE you can actually eat to, and how to set loss, maintenance and gain targets that match how bodies really behave — with our BMR calculator doing the arithmetic at each step.

How to Calculate BMR, Step by Step

1. Gather four honest inputs. Sex, age, height in centimetres and weight in kilograms — weigh yourself in the morning, before food, for the most consistent figure. 2. Run the Mifflin-St Jeor equation. Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5. Women: the same, but − 161 at the end instead of + 5. The structure tells a story: weight and height push the number up because a bigger body costs more to maintain, while each year of age subtracts 5 calories as metabolism gradually slows. 3. Multiply by your activity factor to get TDEE. Sedentary desk work is 1.2, light exercise one to three days a week sits above that, moderate training three to five days a week is 1.55, and very active physical work reaches 1.9. 4. Set your target from TDEE, never from BMR. The calculator returns all three numbers at once — BMR, TDEE, and ready-made targets for losing or gaining about half a kilo per week — so you can see exactly how far apart rest and real life are before you plan a single meal.

Worked Example: From Formula to a Real Day of Eating

Take a 30-year-old man, 175 cm tall, weighing 75 kg, who trains moderately three to five days a week. Weight term: 10 × 75 = 750. Height term: 6.25 × 175 = 1,093.75. Age term: 5 × 30 = 150, subtracted. Add the male constant of 5 and his BMR is 750 + 1,093.75 − 150 + 5 = 1,699 calories a day — what he would burn lying still for 24 hours. Multiply by the moderate activity factor: 1,699 × 1.55 = 2,633 calories of TDEE. That 934-calorie gap between rest and reality is the single most misunderstood number in dieting. Eating at his BMR of 1,699 while living his actual life would be a deficit of over 900 calories — a crash diet wearing a lab coat. His real targets: 2,133 a day to lose about half a kilo a week, 2,633 to maintain, 3,133 to gain at the same pace.

Turning TDEE Into a Target That Works

One kilogram of body fat stores roughly 7,700 calories, so the maths of pace is simple division: a 500-calorie daily deficit adds up to about 3,500 a week, roughly half a kilo. From any TDEE you can build the full ladder — minus 750 for an aggressive short push at about 0.7 kg a week, minus 500 for the steady pace most people sustain best, minus 250 for a slow approach near goal weight that barely feels like dieting, TDEE itself for maintenance, and plus 250 to 500 for a lean gain alongside strength training. Two rules keep the ladder honest. First, protein: at least 1.6 grams per kilo of body weight while dieting, so the weight you lose is fat rather than muscle. Second, recalculation: your TDEE is a moving target that drops as you get lighter, so rerun the numbers after every 3–4 kg lost instead of wondering why progress stalled. If imperial units are your native language, our weight converter handles the kilograms-to-pounds translation before you start.

BMR, TDEE and the Number on the Bathroom Scale

BMR typically accounts for 60–70% of everything you burn; the rest is movement, exercise and the cost of digesting food. That split explains two everyday puzzles. It is why two people of the same weight can eat noticeably different amounts — the one with more muscle burns more at rest, since muscle costs roughly 6 calories per pound per day against about 2 for fat. And it is why activity honesty matters more than formula precision: the same person's TDEE swings by 500 calories or more between a sedentary month and a moderately active one, a bigger effect than any rounding in the equation itself. Pair this guide with our BMI calculator if you want the weight-category context alongside the calorie numbers — the two tools answer different questions, and together they frame a sensible target.

Common Mistakes

Eating to your BMR instead of your TDEE. BMR is a lying-still number; using it as a food target under-fuels an active life by hundreds of calories. Overestimating activity. A busy desk job is still sedentary at 1.2 — feeling rushed is not exercise, and this single error sinks more calorie targets than any other. Setting one target forever. A lighter body burns less; a target that worked at 85 kg becomes maintenance at 78 kg unless you recalculate. Crashing below safe floors. Regularly eating below BMR risks muscle loss, fatigue and nutrient gaps; general guidance keeps women above roughly 1,200 and men above roughly 1,500 calories a day during weight loss, and medical conditions — thyroid, PCOS, pregnancy, diabetes, medication — belong with a doctor or registered dietitian, not a formula. Expecting lab precision. Mifflin-St Jeor lands within about 10% for most adults; treat it as a starting estimate and let two to three weeks of real scale trend fine-tune it.

Frequently Asked Questions

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