BMR Calculator
Use this BMR Calculator to estimate your Basal Metabolic Rate — the number of calories your body burns at complete rest just to keep your heart beating, lungs breathing, and cells working. Combined with your activity level, it gives you your Total Daily Energy Expenditure (TDEE), the calorie target that holds your weight steady. Switch between the Mifflin–St Jeor equation (the modern standard) and the classic Harris–Benedict formula for comparison.
BMR Calculator
Basal Metabolic Rate & daily calorie needs
📐 How BMR Is Calculated
The Mifflin–St Jeor equation, published in 1990, is considered the most accurate predictive formula for healthy adults and is the standard used by the Academy of Nutrition and Dietetics. It calculates BMR from four inputs: weight, height, age, and sex.
Once BMR is known, multiplying it by your activity factor (1.2 to 1.9) gives your Total Daily Energy Expenditure (TDEE) — the calorie level that keeps your weight stable. If imperial units are entered, the calculator automatically converts pounds and feet/inches to kilograms and centimeters before applying the formula.
📊 Activity Multipliers Explained
Your BMR only covers calories burned at rest. To estimate your full daily burn, multiply BMR by a factor that reflects how active you are. Choosing the right level is the single biggest factor in calorie-target accuracy — most people overestimate.
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, little or no exercise |
| Lightly Active | × 1.375 | Light exercise or sport 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 daily training or physical job |
🌐 Mifflin–St Jeor vs. Harris–Benedict
Both formulas estimate the same thing — the calories your body burns at rest — but they were built from different data, decades apart. The toggle in the calculator lets you compare results side by side.
Mifflin–St Jeor (1990)
More accurate for modern populations and the recommended default.
Harris–Benedict (Revised)
The original BMR formula, revised in 1984 by Roza & Shizgal.
Quick guide: If you’re unsure, use Mifflin–St Jeor. Differences between the two formulas are usually within 100–200 calories — well inside the normal day-to-day variation in real energy needs.
⚠️ What BMR Doesn’t Tell You
BMR formulas use just four inputs, so they can’t capture everything that affects metabolism. Treat the number as a starting point, not a fixed budget.
Body Composition
Muscle burns more calories at rest than fat. Two people the same height and weight can have very different real BMRs depending on muscle mass.
Daily Variability
BMR shifts with sleep, stress, temperature, hormones, and recent meals. A single estimate is an average, not a daily exact.
Medical Factors
Thyroid function, medications, pregnancy, and chronic conditions can all raise or lower BMR significantly beyond what formulas predict.
It’s an Estimate
True BMR is measured in a lab using indirect calorimetry. Formula-based BMR is generally accurate within ~10% — close enough for planning, not for prescription.
💡 How to Use Your BMR Result
The most useful number from this calculator isn’t BMR itself — it’s TDEE and the calorie targets built from it. Here’s how to put them to work:
🔗 Related Calculators
BMR is one piece of the metabolism puzzle. These tools help you build the bigger picture of body composition and growth:
