What next?
BMR is your body at rest. Activity and goals sit on top of it.
What your result means
Your BMR is the energy your body would burn lying completely still for twenty-four hours — keeping your heart beating, lungs working, brain running and cells repairing. It is not a target to eat to. It is the floor beneath everything else, and typically accounts for around 60–70% of the calories a moderately active person burns in a day.
Why this one is different
The Mifflin-St Jeor equation is named and written out with its constants spelled out, and the page explains why it is preferred over the older Harris-Benedict equation instead of silently picking one. Metric and imperial input, and the worked example below is computed by script against the live tool, so the figures are proven to match.
Most of your calories are burned doing nothing at all
People assume exercise dominates their daily burn. For all but athletes it does not — an hour of hard training might add a few hundred calories to a base of well over a thousand. That is why sustainable change comes from consistent intake rather than trying to out-train a diet.
BMR also explains why aggressive dieting stalls. Lose weight and BMR falls, because there is less tissue to maintain; the deficit that worked at the start quietly becomes maintenance.
How it works
The Mifflin-St Jeor equation predicts resting energy expenditure from weight, height, age and sex. It was published in 1990 and validated against indirect calorimetry, and is now the equation most dietitians prefer — it is more accurate for modern populations than the older Harris-Benedict formula.
How to use this calculator
- Choose metric or imperial units.
- Select your sex at birth — the equation uses different constants.
- Enter your age, height and weight.
- Read your BMR, then use the TDEE calculator to add your activity level.
Formula
Women: BMR = 10w + 6.25h − 5a − 161
w = weight in kg, h = height in cm, a = age in years. Result in kcal per day.
Example calculation
A 30-year-old man, 178 cm and 78 kg:
BMR = 780 + 1,112.5 − 150 + 5
BMR ≈ 1,748 kcal/day
Frequently asked questions
What is the difference between BMR and RMR?＋
BMR is measured under strict conditions — fasted, fully rested, in a controlled temperature. RMR (resting metabolic rate) is measured under less rigid conditions and comes out around 10% higher. In everyday use the two terms are often used interchangeably.
Should I eat at my BMR to lose weight?＋
No. Eating below your BMR is rarely advisable and is hard to sustain nutritionally. Subtract a moderate deficit from your TDEE — which includes activity — rather than eating at or below the resting floor.
How accurate is the estimate?＋
For most people it lands within about 10% of a measured value. It cannot account for unusual body composition, thyroid conditions or medication, so treat it as a starting point and adjust based on real-world results.
Which BMR formula does this use?＋
The Mifflin-St Jeor equation, which is the one most commonly recommended for healthy adults because it tracks measured resting energy expenditure more closely than the older Harris-Benedict equation for modern body compositions.
Does BMR fall as I lose weight?＋
Yes. A smaller body needs less energy to maintain, so BMR drops as weight comes off. Recalculate every 4-5 kg of change, otherwise your target intake slowly drifts too high.
Why is my BMR lower than a friend's at the same weight?＋
Height, age and sex all enter the equation, and lean mass is the biggest driver of resting energy use. Two people at the same weight with different muscle mass can differ by 150-250 kcal a day.
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Assumptions & limitations
Every figure here comes from a simplified model. Keep these limits in mind when reading your result:
- Uses the Mifflin-St Jeor equation, which assumes a typical body composition for the stated height and weight.
- Very muscular or very lean individuals will burn more than predicted; the equation cannot see body fat percentage.
- Does not account for thyroid conditions, medication, pregnancy or illness.
- Not suitable for children or adolescents, whose energy needs differ substantially.