BMR vs TDEE: What's the Difference?
BMR (Basal Metabolic Rate) is the minimum calories your body needs just to exist: breathing, heartbeat, cell repair, temperature regulation. It assumes you are lying completely still for 24 hours, awake, rested and not digesting a meal. In practice most equations estimate resting metabolic rate (RMR), which is within a few percent of BMR.
TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor. It is the number of calories you actually burn each day, and the number to target when setting calorie goals. Use the calorie calculator to turn it into a goal with macros.
The three formulas
Mifflin-St Jeor (1990)
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Harris-Benedict, revised by Roza and Shizgal (1984)
Men: BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age
Katch-McArdle
BMR = 370 + 21.6 × lean body mass(kg)
Worked example. A 30-year-old woman, 165 cm and 60 kg. Mifflin-St Jeor: 10 × 60 = 600, 6.25 × 165 = 1,031.25, 5 × 30 = 150. So 600 + 1,031.25 − 150 − 161 = 1,320 kcal a day. With moderate exercise (× 1.55) her TDEE is about 2,046 kcal. If she knows her body fat is 25%, her lean mass is 45 kg and Katch-McArdle gives 370 + 21.6 × 45 = 1,342 kcal.
Mifflin-St Jeor vs Harris-Benedict
| Formula | Published | Accuracy | Best For |
|---|---|---|---|
| Mifflin-St Jeor | 1990 | Most often within 10% of measured RMR in a 2005 systematic review | General adult population, recommended by the Academy of Nutrition and Dietetics |
| Harris-Benedict (revised) | 1919, revised 1984 | Within 10% less often than Mifflin-St Jeor in the same review | Historical reference, still common in older apps |
| Katch-McArdle | Exercise physiology textbook equation | Only as good as your body fat estimate | Lean or very muscular people who know their body fat |
The Mifflin-St Jeor equation is endorsed by the Academy of Nutrition and Dietetics as the most accurate predictor of resting metabolic rate for adults without known body composition data. A 2005 systematic review by Frankenfield and colleagues found it predicted RMR within 10% of the measured value in more non-obese and obese adults than the other equations tested. Individual errors can still be larger, so treat any result as a starting point.
About the activity multipliers
The 1.2 to 1.9 factors in the table are the multipliers most calculators use. They are rough. The FAO/WHO/UNU expert report on human energy requirements describes a sedentary or lightly active lifestyle as a physical activity level of 1.40 to 1.69 times BMR, so 1.2 is a conservative floor. The best check is your own weight trend: if your weight is stable over a few weeks, what you eat is your real TDEE.
What raises or lowers BMR
Size and lean mass matter most: a bigger body with more muscle burns more at rest. BMR falls slowly with age, partly because muscle mass falls. Men usually have a higher BMR than women of the same weight because they carry more lean mass. Thyroid disorders, some medicines, fever and pregnancy also change it. If you are losing or gaining weight without an explanation, see a doctor rather than adjusting a calculator.