BMR Calculator
Find your Basal Metabolic Rate — the calories your body burns at complete rest — using three trusted formulas: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle. Enter your details in metric or imperial units and see your daily calorie needs across activity levels.
Enter your age, sex, height, and weight to estimate your Basal Metabolic Rate. Choose a formula — Mifflin-St Jeor is the modern standard; Katch-McArdle uses body fat % for leaner, more athletic bodies.
| Activity Level | Description | Calories / Day |
|---|
* BMR estimates are based on population formulas and are for general educational purposes only — they are not medical or nutritional advice. Individual metabolism varies with genetics, muscle mass, hormones, and health conditions. The activity-level figures are rough maintenance estimates. Consult a qualified healthcare professional or registered dietitian before making changes to your diet or exercise routine.
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What Is BMR (Basal Metabolic Rate)?
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest, just to keep you alive — powering your heart, lungs, brain, kidneys, and other vital functions. It's the energy you'd use if you stayed in bed all day and did nothing. For most people, BMR accounts for roughly 60–75% of all the calories burned in a day, making it the single biggest part of your total energy needs.
A BMR calculator estimates this number from your age, sex, height, and weight. Our tool goes further than most by offering three established formulas — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle — and showing how your BMR scales into daily calorie needs once activity is included.
How to Use This BMR Calculator
- Choose units — metric (cm, kg) or imperial (ft/in, lb).
- Pick a formula — Mifflin-St Jeor is the modern recommended default.
- Enter age and sex — both affect resting metabolism.
- Enter height and weight.
- For Katch-McArdle — also enter your body fat %, which makes the estimate more accurate for lean, muscular bodies.
The BMR Formulas Explained
Different equations suit different people. Here's how the three compare:
Mifflin-St Jeor (women): BMR = 10×kg + 6.25×cm − 5×age − 161
Harris-Benedict (men): BMR = 88.362 + 13.397×kg + 4.799×cm − 5.677×age
Harris-Benedict (women): BMR = 447.593 + 9.247×kg + 3.098×cm − 4.330×age
Katch-McArdle: BMR = 370 + 21.6 × lean body mass (kg)
- Mifflin-St Jeor — introduced in 1990 and widely considered the most accurate for the general population. Our default.
- Harris-Benedict — a classic equation (revised 1984); slightly less precise but still common.
- Katch-McArdle — uses lean body mass (from body fat %), so it's the best choice for athletic or very lean individuals where muscle mass drives metabolism.
BMR vs RMR vs TDEE: What's the Difference?
- BMR (Basal Metabolic Rate): calories at complete rest, measured under strict conditions (fasted, fully rested). The baseline.
- RMR (Resting Metabolic Rate): similar but measured in less strict conditions; usually about 10% higher than BMR. The terms are often used interchangeably.
- TDEE (Total Daily Energy Expenditure): your BMR multiplied by an activity factor — the total calories you actually burn in a day, including movement and digestion.
Once you know your BMR, the natural next step is your TDEE. Use our TDEE Calculator to factor in your activity level, then our Calorie Calculator to set targets.
How BMR Becomes Daily Calorie Needs
To turn BMR into the calories you burn on a typical day, multiply it by an activity factor:
| Activity Level | Multiplier | Who It Fits |
|---|---|---|
| Sedentary | × 1.2 | Little or no exercise, desk job |
| Lightly active | × 1.375 | Light exercise 1–3 days/week |
| Moderately active | × 1.55 | Moderate exercise 3–5 days/week |
| Very active | × 1.725 | Hard exercise 6–7 days/week |
| Extra active | × 1.9 | Very hard exercise & physical job |
What Affects Your BMR?
- Muscle mass: muscle burns more energy at rest than fat, so more lean mass raises BMR.
- Age: BMR gradually declines with age as muscle mass decreases.
- Sex: men typically have higher BMR due to greater average muscle mass.
- Body size: taller, heavier bodies have more tissue to maintain.
- Genetics & hormones: thyroid function and other factors play a role.
- Crash dieting: very low intakes can lower BMR over time.