Why use Mifflin-St Jeor instead of Harris-Benedict?

Mifflin-St Jeor was validated on a more modern population and is generally accepted as the more accurate of the two general-purpose equations for adults, typically landing within about 10% of measured resting energy expenditure.

What is the difference between BMR and RMR?

Resting metabolic rate is measured under less strict conditions than basal metabolic rate and usually comes out a few percent higher. For everyday planning the two are used interchangeably.

Does BMR fall as I lose weight?

Yes. A smaller body needs less energy, so recalculate every few kilograms rather than sticking with your starting number.

BMR Calculator

Your basal metabolic rate is the energy your body burns keeping you alive at rest: breathing, circulation, cell repair and brain activity. It is the foundation of any calorie target and typically accounts for 60–70% of daily energy use.

Fill in the fields above and select Calculate to see your result and the full working.

Please note: Health calculators on this site provide general estimates based on population-level formulas. They are not medical advice and cannot account for your individual medical history. Speak to a qualified healthcare professional before making decisions about diet, medication or training.

Formula used

Mifflin-St Jeor: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 for males, − 161 for females

How to use this calculator

Pick your unit system and enter height and weight.
Add your age in years and sex at birth — both change the constants in the equation.
Calculate to see resting energy expenditure in kilocalories per day.
Multiply it by an activity factor, or use the TDEE calculator, to get a full daily target.

Example calculation

A 30-year-old man, 175 cm, 70 kg:

(10 × 70) + (6.25 × 175) − (5 × 30) + 5

= 700 + 1,093.75 − 150 + 5

= 1,648.75, so roughly 1,650 kcal per day at rest.

What does this result mean?

BMR is the floor of your energy needs, measured as if you spent all day lying still in a warm room. Nobody actually burns only their BMR: everyday movement, digestion and exercise sit on top. Eating far below BMR for long periods is associated with muscle loss and low energy availability, which is why most guidance sets calorie deficits relative to total daily expenditure rather than BMR.

Frequently asked questions

Why use Mifflin-St Jeor instead of Harris-Benedict?: Mifflin-St Jeor was validated on a more modern population and is generally accepted as the more accurate of the two general-purpose equations for adults, typically landing within about 10% of measured resting energy expenditure.
What is the difference between BMR and RMR?: Resting metabolic rate is measured under less strict conditions than basal metabolic rate and usually comes out a few percent higher. For everyday planning the two are used interchangeably.
Does BMR fall as I lose weight?: Yes. A smaller body needs less energy, so recalculate every few kilograms rather than sticking with your starting number.

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