Mifflin-St Jeor formula with activity level
BMR (Basal Metabolic Rate) is the energy your body needs at rest — for heartbeat, breathing, cell maintenance. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor and equals your total daily calorie burn. To maintain weight, eat your TDEE.
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + s, where s = +5 for men and −161 for women. Published in 1990, this formula is considered more accurate than the older Harris-Benedict equation and is preferred by nutritionists today.
1 kg of body fat equals about 7,700 kcal. A moderate 500 kcal/day deficit yields roughly 0.5 kg/week of weight loss. Deficits above 750-1000 kcal/day are not recommended — risk of muscle loss, hormonal issues and yo-yo dieting. For muscle gain, a surplus of 250-500 kcal/day is plenty.
Basal metabolic rate (BMR) describes the energy your body needs at complete rest — fasted, lying down, in a thermoneutral environment. This share covers heartbeat, breathing, cell division, hormone production and brain activity and makes up roughly 60 - 75 % of daily expenditure in sedentary people. TDEE (Total Daily Energy Expenditure) is BMR plus all movement and digestion costs: the thermic effect of food (TEF, about 10 % of intake), non-exercise activity (NEAT — stairs, gestures, standing) and exercise (EAT — deliberate training).
This calculator uses the Mifflin-St Jeor equation (Mifflin et al., American Journal of Clinical Nutrition 1990). Comparative studies — e.g. Frankenfield et al. 2005 in the Journal of the American Dietetic Association — show it is more accurate than the older Harris-Benedict formula (1919, revised 1984) for most adults: the average deviation from indirectly measured BMR is below 10 %. For people with unusual body composition (very high muscle mass, severe obesity) the Katch-McArdle formula (based on fat-free mass) is more accurate but requires a measured body-fat percentage.
The activity factor multiplies BMR to estimate total daily expenditure. The five common levels (1.2 / 1.375 / 1.55 / 1.725 / 1.9) come from FAO/WHO recommendations and are used in most international nutrition apps. Important: these factors often overstate the requirement because they assume an 'average' activity per level. If you have actual step-count or training data, you are often closer with one level lower than your gut would pick.
Mifflin-St Jeor derives BMR from weight (kg), height (cm), age (years) and sex. It is then scaled by the activity factor to TDEE.
Mifflin-St Jeor (1990):
BMR (male) = 10*kg + 6.25*cm - 5*age + 5
BMR (female) = 10*kg + 6.25*cm - 5*age - 161
TDEE = BMR * activity_factor
activity_factor:
1.2 sedentary
1.375 light (1-3 trainings/week)
1.55 moderate (3-5)
1.725 active (6-7)
1.9 very active (twice/day, hard labor)Five realistic profiles, worked through:
Do not rely solely on this number if you have thyroid disorders, type 1 or insulin-treated type 2 diabetes, cardiac disease, are pregnant or breastfeeding, are under 18, have had bariatric surgery or follow a very restrictive diet. Anyone who chronically eats far below BMR (for months on end) can run a 5 - 15 % lower actual expenditure through adaptive thermogenesis — the formula then overestimates. Indirect calorimetry in a metabolic clinic gives the most accurate result. This page is an informational estimate and not a substitute for medical or nutritional advice; for health questions consult your physician or a qualified dietitian.