What your body burns doing nothing.
Your basal metabolic rate is the energy you spend simply being alive — before you stand up, walk anywhere or train. It is the foundation every calorie target is built on, and it is bigger than most people expect.
The two equations
Mifflin-St Jeor is the default. It was published in 1990 and validated against indirect calorimetry in modern populations, and it replaced the 1919 Harris-Benedict equation as the recommended predictor for exactly that reason.
Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Katch-McArdle takes a different route. Instead of guessing at body composition from height and weight, it prices the tissue that actually burns the energy:
Notice that it has no term for sex — the difference between men and women in the first equation is largely a proxy for a difference in body composition, which the second measures directly. That is why it is the better choice for a very lean or very muscular person, and the worse choice for anyone guessing at their body fat.
Why your real BMR may differ
These are population regressions, and an individual can sit ten percent either side of the prediction without anything being wrong. Thyroid function, a long history of dieting, genetics and how much lean mass you carry all move it. Medication and illness move it too.
The practical answer is not to chase a more precise equation. It is to use this figure as a starting point, eat consistently for a fortnight, and let your actual weight trend tell you where your metabolism really sits. The scale is the measurement; the equation is just the opening guess.
Questions people ask
What is BMR?
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Basal metabolic rate is the energy your body spends doing nothing at all — running your heart, brain, kidneys and liver, and holding your temperature. It is measured lying still, awake, after an overnight fast. For most people it is 60 to 70% of everything they burn in a day.
What's the difference between BMR and TDEE?
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BMR is the floor; TDEE — total daily energy expenditure — is the whole thing. TDEE is your BMR plus the energy you spend digesting food, moving around during the day, and training. This page shows both: the headline is your BMR, and the table underneath applies each activity multiplier to reach TDEE.
Should I eat my BMR?
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No. Almost nobody should eat at their BMR, because almost nobody spends the day lying motionless. Eating at BMR while living a normal life is a large, unintentional deficit. Use your TDEE as the reference point and adjust from there — that is what the calorie calculator does.
Which equation is more accurate — Mifflin-St Jeor or Katch-McArdle?
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Mifflin-St Jeor is the better default because it only needs height, weight, age and sex. Katch-McArdle works from lean body mass instead, so it is more accurate for people who are unusually lean or unusually muscular — but it is only as good as your body fat estimate, and a bad body fat number makes it worse than Mifflin. If you do not know your body fat with reasonable confidence, use Mifflin.
Can I speed up my metabolism?
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Not dramatically, and not with food timing, green tea or cold showers. The lever that genuinely works is muscle: lean tissue is metabolically active, so adding it raises your BMR permanently, and resistance training also protects the BMR you have while you diet. The effect is modest but real, and it compounds.
Related calculators
A number is a starting point, not a plan.
This calculator can tell you where you are. It cannot watch your form, adjust when your knee flares up, or keep you consistent in week six. If you want that part, we run a private studio in Kharadi and the first session is free.
This tool provides general fitness and nutrition information for healthy adults aged 18 and over. It is not medical advice, diagnosis or treatment. Speak to a doctor before starting any new exercise or nutrition programme, particularly if you have a health condition, are pregnant or post-partum, or have a history of disordered eating.