About BMR
Every calorie plan starts here whether it says so or not: BMR is the floor of your energy budget — what you'd burn in bed all day — and every “calories to lose weight” number is built by multiplying it up for activity and subtracting a deficit. Know the floor and the rest of the arithmetic stops being mysterious.
Enter sex, age, height, and weight for your BMR, the per-hour resting burn, and the equation's working. The number is the input to everything else: multiply by an activity factor for maintenance (that's TDEE), then adjust for goals.
The full daily-burn version with activity built in is the TDEE Calculator.
The Mifflin-St Jeor Equation
One linear equation, sex adjusting only the constant:
Men: BMR = 10×kg + 6.25×cm − 5×age + 5 Women: BMR = 10×kg + 6.25×cm − 5×age − 161
Worked example: a 30-year-old man, 175 cm and 70 kg: 700 + 1,093.75 − 150 + 5 = 1,649 kcal/day — about 69 kcal per hour of just existing. The same stats female: 1,483. Mifflin et al. validated it against measured resting expenditure in 1990 (cited below); dietetic practice adopted it as the default.
From BMR to Daily Calories
Multiply BMR by an activity factor for maintenance calories — the standard multipliers on the worked example's 1,649:
| Lifestyle | Factor | Maintenance (example) |
|---|---|---|
| Sedentary (desk, little exercise) | 1.2 | 1,979 kcal |
| Light (1–3 workouts/week) | 1.375 | 2,267 kcal |
| Moderate (3–5 workouts/week) | 1.55 | 2,556 kcal |
| Active (6–7 workouts/week) | 1.725 | 2,845 kcal |
| Very active (physical job + training) | 1.9 | 3,133 kcal |
Most people overestimate their factor by one tier — an office worker who trains three evenings is “light-to-moderate,” not “active.” When in doubt, pick lower and adjust to results.
What Moves Your BMR
The levers, in order of practical size: body weight itself (each kg is ~10 kcal/day in the equation — weight loss genuinely lowers BMR), muscle mass (the biggest lever you control — muscle burns more at rest than fat, which is why resistance training protects metabolism during dieting), age (the −5/year term reflects gradual decline, much of it muscle loss rather than time itself), and sex differences in composition.
What doesn't meaningfully move it: metabolism-boosting foods and supplements (effects are trivial or transient), meal timing, and “starvation mode” as popularly imagined — severe restriction does trigger adaptive slowing, but of modest size. If a measured or suspected BMR sits far off the estimate, thyroid function is the medical question worth asking.