BMR Calculator
Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest.
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How to use this calculator
The Mifflin-St Jeor equation is the most accurate BMR formula for most adults.
- 1
Enter your weight in kilograms.
- 2
Enter your height in centimetres.
- 3
Enter your age in years.
- 4
Select your biological sex.
- 5
Select your typical activity level.
- 6
The result shows your BMR (calories at rest) and TDEE (total daily energy expenditure).
Frequently asked questions
Which BMR formula does this calculator use?
Mifflin-St Jeor: 10 × weight in kg + 6.25 × height in cm − 5 × age in years, then +5 for male or −161 for female. There is no body-fat input, so it does not use Katch-McArdle or the Harris-Benedict equation.
How does it get from BMR to maintenance calories?
It multiplies BMR by the activity factor you choose: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. The result is labelled TDEE (total daily energy expenditure) and is rounded to the nearest kilocalorie.
What are the lose and gain figures?
They are simply maintenance minus 500 and maintenance plus 500 kcal per day. The offset is fixed and is not scaled to your size, and the calculator does not predict how much weight you will change over time.
Does the calculator stop me from eating too little?
No. It applies the 500 kcal subtraction without any floor, so a small, sedentary person can see a low figure. For the 60 kg woman in the worked example the lose figure is 1,281 kcal. Very low intakes call for advice from a doctor or dietitian rather than a calculator.
Why does it ask for biological sex?
The equation has a different constant for each: +5 for male and −161 for female, a gap of 166 kcal a day at the same weight, height and age. Any other value than male is treated as female in the code.
Which units does it expect?
Kilograms, centimetres and years. Pounds and feet-and-inches are not converted, and the fields have no range checks, so an implausible entry such as a height typed in inches returns an implausible result.
How reliable is the number for me personally?
It is an estimate for a typical adult. Muscle mass, age-related changes, medical conditions and the activity multiplier you choose all move real energy use away from the formula. Choosing the activity level honestly matters, because it changes TDEE by hundreds of calories. This is general information, not medical advice.
BMR and TDEE calculator — the Mifflin-St Jeor equation
What the calculation does
Basal metabolic rate is the energy your body would use at complete rest. The calculator estimates it with the Mifflin-St Jeor equation, published in 1990, which adds 10 kcal per kilogram of weight and 6.25 kcal per centimetre of height, subtracts 5 kcal per year of age, and then applies a constant of +5 for men or −161 for women. It then multiplies that figure by an activity factor to give a maintenance estimate and shows values 500 kcal above and below it.
Worked examples
These three cases were run through the calculator exactly as shown.
| Person | BMR | TDEE | TDEE − 500 | TDEE + 500 |
|---|---|---|---|---|
| Man, 70 kg, 175 cm, 30 y, moderately active (1.55) | 1,649 | 2,556 | 2,056 | 3,056 |
| Woman, 60 kg, 165 cm, 35 y, lightly active (1.375) | 1,295 | 1,781 | 1,281 | 2,281 |
| Man, 85 kg, 180 cm, 45 y, sedentary (1.2) | 1,755 | 2,106 | 1,606 | 2,606 |
How much the activity level changes the answer
BMR does not depend on how active you are, but maintenance calories do, and the activity step is a judgement call. Keeping the first example person fixed at 1,649 kcal BMR, the five choices give 1,979 kcal (1.2), 2,267 kcal (1.375), 2,556 kcal (1.55), 2,844 kcal (1.725) and 3,133 kcal (1.9). That spread is more than 1,100 kcal, so picking the level that matches a typical week, not your most active one, is worth the thought.
Reading the lose and gain lines
The plus and minus 500 figures are a convenient planning offset, not a prescription and not a forecast. The calculator does not model how your metabolism responds to eating less or more, and it will happily show a low number for a small person. Treat them as starting points to test against real-world changes in weight and energy over several weeks, and adjust from there.
What this estimate leaves out
Body composition is the main omission: two people with identical weight, height, age and sex can burn different amounts if one has more muscle. Pregnancy, breastfeeding, thyroid conditions, medication and recovery from illness can also change energy needs, and none of them are inputs. If you are managing a medical condition or aiming for a large change in weight, a doctor or registered dietitian can set a target that fits your situation.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →