BMR calculator and what resting burn really is
Basal metabolic rate is the energy your body spends just staying alive: breathing, circulation, cell repair, keeping warm. It is the largest share of what you burn each day.
BMR calculator
Mifflin-St Jeor equation. An estimate from population averages, not a measurement of you.
What BMR is
BMR is measured at complete rest, fasted, in a neutral-temperature room. It covers the work your organs do with no movement at all. For a typical adult that is 1,200 to 2,000 kcal a day, and it accounts for 60 to 70% of total daily burn in anyone who is not an athlete.
The formula
The calculator uses Mifflin-St Jeor, which outperformed the older Harris-Benedict equation in validation studies and is the one most dietitians use.
BMR (women) = 10 x kg + 6.25 x cm - 5 x age - 161
What moves BMR
- Lean mass. Muscle burns more at rest than fat. Two people at the same weight can differ by a few hundred calories.
- Age. BMR drifts down roughly 1 to 2% per decade after your twenties, mostly from lost muscle.
- Size. A bigger body has more tissue to maintain, so BMR rises with weight and height.
- Sleep, illness and heat. Short-term swings of a few percent are normal.
BMR versus resting energy on an Apple Watch
Apple Health has a resting energy field that is the Watch's own estimate of your BMR, built from your height, weight, age and sex in the Health profile and spread across the day. It is close to the Mifflin-St Jeor number but updates as your profile changes, and because it lands in Health hour by hour you can see how much of today's burn is resting versus active.
Total Calories shows that split on its dashboard and adds the two halves into one daily total, which is the number most people actually want when they ask about their BMR: not the resting figure alone, but what it means for how much they can eat.
From BMR to a calorie target
BMR is a floor, not a target. Eating below it for long is neither necessary nor pleasant. Multiply by an activity factor, or better, read your measured daily total, and set a deficit or surplus from there. The TDEE guide covers that step.
Informational only, not medical advice.
Common questions
Is BMR the same as resting metabolic rate?
Nearly. RMR is measured under slightly looser conditions and runs about 10% higher than true BMR. Fitness apps, including Apple Health's resting energy, use the two interchangeably.
Should I eat my BMR to lose weight?
No. BMR is the energy you burn at complete rest. Your real daily burn is higher, so set a moderate deficit from your total daily expenditure, not from BMR.
Why is my Apple Watch resting energy different from the calculator?
Apple uses its own model and the height, weight, age and sex in your Health profile. Small differences of 50 to 150 kcal are expected. Keep your Health profile current and the number tracks you better than any formula.