Estimating BMR — Mifflin-St Jeor and Harris-Benedict

Basal metabolic rate (BMR) is the energy expended at complete rest to sustain life (breathing, circulation, cell maintenance). It is the largest component of daily energy use, typically 60–70% of total expenditure. Resting metabolic rate (RMR) is a slightly less strict measurement but is often used interchangeably. BMR is estimated from sex, weight, height, and age using prediction equations:

Mifflin-St Jeor (1990) — the recommended default, validated as the most accurate for modern populations (within ~10% of measured for most people):

• Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age yr) + 5
• Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age yr) − 161

Harris-Benedict (1919, revised 1984) — older and tends to overestimate by ~5–15% in sedentary people:

• Men: BMR = 88.362 + (13.397 × weight kg) + (4.799 × height cm) − (5.677 × age yr)
• Women: BMR = 447.593 + (9.247 × weight kg) + (3.098 × height cm) − (4.330 × age yr)

These are estimates, not measurements — individual metabolism varies with lean mass, genetics, and history (equations using lean body mass, e.g. Katch-McArdle, can be more accurate for lean, muscular people). BMR is the starting point; multiply by an activity factor to get total daily energy expenditure (see tdee and activity-factors).

• BMR = resting energy to stay alive; ~60–70% of daily expenditure.
• Mifflin-St Jeor (recommended): M = 10W + 6.25H − 5A + 5; W = 10W + 6.25H − 5A − 161 (kg, cm, yr).
• Harris-Benedict (older): overestimates ~5–15% in sedentary people.
• Equations are estimates; lean-mass formulas (Katch-McArdle) suit muscular individuals.
• BMR × activity factor = TDEE.

• tdee — scaling BMR to total daily expenditure.
• activity-factors — the multipliers applied to BMR.
• calorie-targets — turning TDEE into goal-based calorie targets.
• caloric-intake-factors — what drives individual calorie needs.