What BMR covers
Basal metabolic rate is the energy cost of simply existing: heartbeat, breathing, brain activity, keeping warm, repairing cells. For most people it is 60–70% of everything they burn in a day — more than exercise, usually by a wide margin. That is why two people of different sizes can eat the same food with very different results.
Mifflin-St Jeor vs Harris-Benedict
Both estimate the same thing from the same inputs. Harris-Benedict dates from 1919 and tends to read a little high for modern, more sedentary bodies; Mifflin-St Jeor (1990) was fitted on newer data and is the one the American Dietetic Association recommends. We show both — if they disagree by more than a hundred calories, trust the Mifflin number.
From BMR to a calorie target
BMR alone is not an eating target — you also move. The table above multiplies your BMR through the standard activity ladder, from sedentary (×1.2) to extra active (×1.9). Pick the row that honestly matches your week and you have your maintenance calories; our TDEE and macro calculators take it from there.
Frequently asked questions
Why is my BMR lower than my friend's?
BMR scales mainly with body size and lean mass, then falls slowly with age and runs lower for women at the same size. Two people the same weight can differ by hundreds of calories if one carries more muscle.
Can I raise my BMR?
The only lever that meaningfully moves it is gaining muscle — each kilogram of lean mass burns roughly 13 kcal per day at rest. Crash dieting moves it the other way: severe restriction lowers BMR as the body adapts.
Is this medical advice?
No. The Mifflin-St Jeor equation, which validation studies favour over the older Harris-Benedict. Thyroid conditions and several medications shift metabolic rate well beyond what any equation predicts.
Is my data stored or sent anywhere?
No. Nothing about your body is transmitted anywhere.
Something wrong with this tool, or an idea for it? Tell us