Chapter 01 · The floor
What BMR actually is
Your Basal Metabolic Rate is the floor of your daily energy needs. It is the calories your body burns to keep you alive at rest: breathing, beating, repairing, signaling. For most adults, BMR accounts for 60% to 75% of total daily energy expenditure. The rest comes from physical activity and the thermic effect of food.1
*12 month plan, billed once for the term when a physician approves. Renews each term.
The Mifflin-St Jeor equation was published in 1990 and is now the recommended prediction equation for the general adult population. For men, BMR equals 10 times kilograms of body weight, plus 6.25 times height in centimeters, minus 5 times age in years, plus 5. For women, substitute minus 161 for that trailing constant. The constants encode the average sex-specific difference in lean mass.1
| Day type | Rough multiplier | What it represents |
|---|---|---|
| BMR (at rest) | The base | Energy burned at complete rest |
| Sedentary day | BMR times 1.2 | Little or no exercise |
| Moderate day | BMR times 1.55 | Some regular activity |
| Very active day | BMR times 1.725 | Frequent hard training |
Relative multipliers, not your personal figures.
Chapter 02 · The equation
Why Mifflin and not Harris-Benedict
The original prediction equation was Harris-Benedict (1919, revised in 1984). Harris-Benedict overestimates BMR for most modern adults by roughly 5%, primarily because body composition has shifted across the century since its derivation. Mifflin-St Jeor was derived from a more contemporary cohort and validated against indirect calorimetry. A 2005 systematic review recommended Mifflin-St Jeor as the most accurate predictor for the non-obese adult general population.2
Start here · one question
What's your goal weight?
Choose a goal to discuss with your clinician. You can change it in your intake.
The point: BMR is not the number you eat. It is the number you start from. Add activity to reach your daily target. Individual results vary.
Chapter 03 · The next step
What to do with this number
BMR is the number you start from. To estimate your total burn (TDEE), multiply BMR by an activity factor between 1.2 (sedentary) and 1.9 (extra active). To lose weight, subtract 250 to 500 kcal per day from your TDEE for a steady half to one pound per week. Any larger deficit is best done with a physician watching for muscle loss and adaptation. The physician, not this calculator, makes the clinical decision. Individual results vary.
