Calorie Calculator

Every calorie calculator starts from a basal metabolic rate (BMR) equation, and the choice of equation changes the answer by meaningful amounts. This tool uses Mifflin-St Jeor, published in 1990 from measurements of 498 adults: for men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women the final constant is −161 instead of +5. The American Dietetic Association's 2005 systematic review compared the popular equations against measured resting metabolism and found Mifflin-St Jeor predicted within 10% of the true value more often than any rival, which is why it has become the clinical default. The older alternative you will still meet everywhere is Harris-Benedict, derived in 1919 from a small early-20th-century cohort and revised by Roza and Shizgal in 1984. The revised male form is BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age; the female form is 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age. Harris-Benedict tends to overestimate modern sedentary adults by roughly 5%, partly because its reference population was leaner and more active. For the same 30-year-old, 175 cm, 70 kg man, Mifflin-St Jeor gives 1,649 kcal and revised Harris-Benedict gives 1,696 kcal — a 47 kcal/day spread that compounds to about 17,000 kcal per year. A third formula, Katch-McArdle (370 + 21.6 × lean mass in kg), ignores total weight entirely and is the better choice if you know your body-fat percentage from a DEXA or InBody scan, especially for very muscular or very lean people whom weight-based formulas misjudge.

Male, 30 years, 175 cm, 70 kg

Mifflin-St Jeor:
  10 x 70          =  700.00
  + 6.25 x 175     = 1093.75
  - 5 x 30         = -150.00
  + 5              =    5.00
  BMR              = 1648.75  ->  ~1649 kcal/day

Harris-Benedict (1984 revision):
  88.362 + 13.397 x 70 + 4.799 x 175 - 5.677 x 30
  = 88.362 + 937.79 + 839.825 - 170.31
  = 1695.67        ->  ~1696 kcal/day  (+47 vs MSJ)

BMR is only what your body burns lying still; total daily energy expenditure (TDEE) multiplies it by an activity factor. The standard ladder — 1.2 sedentary, 1.375 lightly active (1–3 workouts/week), 1.55 moderately active (3–5), 1.725 very active (6–7), 1.9 for physical jobs plus training — descends from mid-20th-century nutrition research and FAO/WHO energy requirement reports. The single most common mistake is grading yourself one rung too high: an office worker who lifts weights three evenings a week feels "very active" but arithmetically lands at 1.375–1.55, because 45 minutes of exercise cannot outweigh 15 sedentary waking hours. When in doubt, pick the lower factor, run it for three or four weeks, and let the scale arbitrate. The wildcard the multipliers compress is NEAT — non-exercise activity thermogenesis, the energy of walking, standing, fidgeting, and household work. Research by James Levine at the Mayo Clinic showed NEAT can differ by many hundreds of kilocalories per day between two people with identical BMR and gym habits, which is why a delivery courier and a programmer of the same size need genuinely different multipliers, not the same "moderate" label. Be equally skeptical of gadget numbers: a 2017 Stanford evaluation of seven consumer wrist wearables found heart-rate tracking respectable but energy-expenditure estimates off by 27% to 93%. Using the example from the previous section, a 1,649 kcal BMR at the 1.55 multiplier yields a TDEE near 2,556 kcal — that number is a starting hypothesis to test against real-world weight change, not a verdict.

The weight-loss and weight-gain targets above apply a plus-or-minus 500 kcal adjustment, which comes from the famous rule that one pound (0.45 kg) of body fat stores about 3,500 kcal: a 500 kcal daily deficit should therefore melt one pound per week. The rule traces to a 1958 paper by Max Wishnofsky, and it is approximately right — but only for the first weeks, and only on average. Two effects bend the line. First, the initial drop is exaggerated by water: each gram of stored glycogen binds roughly 3 grams of water, so depleting carbohydrate stores in week one can shed a fast kilogram that is not fat and returns just as fast. Second, metabolic adaptation kicks in: as you lose weight, a smaller body burns less, and the body additionally down-regulates beyond what the size change predicts. The famous 2016 follow-up study of "The Biggest Loser" contestants found their resting metabolism about 500 kcal/day below expectation six years after the show. A static 500-kcal deficit therefore produces a decelerating curve, not a straight line — which is why the US NIH built its Body Weight Planner around a dynamic model instead. Sensible pacing guidelines: aim to lose no more than 0.5–1% of body weight per week, avoid eating chronically below your calculated BMR, and prioritize protein (commonly cited targets run around 1.2–1.6 g per kg of body weight during a deficit) to protect muscle. If progress stalls for three or more weeks, recalculate — your BMR is now that of a lighter person — rather than slashing further.

TDEE 2556 kcal, target: lose ~0.5 kg/week

  Deficit:   2556 - 500 = 2056 kcal/day
  Weekly:    500 x 7    = 3500 kcal  ~  0.45 kg of fat

Reality check over 12 weeks (why the line bends):
  Week 1 : -1.4 kg  (fat + glycogen water, feels amazing)
  Week 4 : -0.5 kg  (mostly fat, on script)
  Week 12: -0.3 kg  (lighter body + adaptation burns less)
  Fix    : recalculate BMR at the new weight, adjust deficit

Every number in this pipeline carries error, and the errors stack. The BMR equation itself is ±10% for most people, so a displayed 1,649 kcal legitimately spans roughly 1,480 to 1,810. Food labels add more: US FDA rules tolerate up to 20% deviation in stated calories, restaurant portions vary batch to batch, and dietary-intake research consistently finds people under-report what they eat — commonly by 20–30%, more among heavier participants. Stack a 10% formula error on a 20% logging error and honest-looking arithmetic can be off by several hundred kilocalories a day. The productive response is not more decimal places but better feedback loops. Weigh yourself under consistent conditions (same time of day, same clothing state), average over a week to smooth water noise, and compare the trend against your target; adjust intake in 100–200 kcal steps every few weeks rather than lurching. Recalculate here after every 4–5 kg of change, and when your training volume or job activity shifts. Some situations belong with professionals rather than calculators. If you are pregnant or breastfeeding, under 18, over 65, managing diabetes, thyroid disease, or another metabolic condition, or have any history of disordered eating, generic TDEE arithmetic can be misleading or actively harmful. The figures on this page are population-level estimates for general information — they are not medical or nutritional advice, and a physician or registered dietitian can tailor targets to blood work, medication, and history in a way no formula can.