BMR Calculator
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Calculate your Basal Metabolic Rate — the calories your body burns at rest. Uses the Mifflin-St Jeor equation.
Basal Metabolic Rate (BMR)
0 cal/day
Calories burned at complete rest
Based on Mifflin-St Jeor equation — the most accurate formula for most adults.
📐 Formula
Male BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5. Female: same but −161 instead of +5. TDEE = BMR × Activity Factor
How to Use the BMR Calculator
Enter your age, sex, height, and weight
These four inputs are the only variables in the Mifflin-St Jeor formula. Use your current weight, not a goal weight.
Select your activity level
Choose the activity multiplier that best reflects your typical week: sedentary (desk job, little exercise), lightly active (exercise 1–3 days), moderately active (exercise 3–5 days), very active (hard exercise 6–7 days), or extra active (physical job + exercise).
Read your BMR and TDEE
BMR is your calorie baseline at rest. TDEE is your actual daily calorie requirement. Use TDEE for any diet or weight management planning.
Adjust for your goal
Subtract 500 calories from TDEE for approximately 0.5kg/week weight loss. Add 250–500 calories for muscle gain. Never eat below your BMR for extended periods.
BMR vs TDEE: The Critical Difference
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to maintain heart function, breathing, temperature regulation, and cellular repair. It accounts for 60–75% of total daily calorie burn for most people. TDEE (Total Daily Energy Expenditure) adds activity on top: exercise, walking, non-exercise activity thermogenesis (NEAT — fidgeting, standing, gesturing), and the thermic effect of food (digesting food burns ~10% of its calories).
For weight management, TDEE is the number that matters. Eating at TDEE maintains weight. Eating below it creates a deficit; above it, a surplus. BMR alone significantly underestimates calorie needs and should never be used as a weight-loss calorie target.
The Mifflin-St Jeor Formula: Why It's the Most Accurate
The Mifflin-St Jeor equation, developed in 1990, consistently outperforms older formulas (Harris-Benedict 1919, Katch-McArdle) in validation studies. It is accurate within ±10% for approximately 80% of adults. The formula: Male BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Female: same but −161 instead of +5. Example: a 35-year-old woman, 65kg, 168cm: (10×65) + (6.25×168) − (5×35) − 161 = 650 + 1,050 − 175 − 161 = 1,364 calories/day BMR. Multiply by activity factor (1.375 for lightly active) = 1,876 TDEE.
Why BMR Changes Over Time
BMR declines approximately 1–2% per decade from age 20 onwards, primarily due to gradual muscle mass loss (sarcopenia). At 60, BMR may be 10–15% lower than at 20 with the same height and scale weight — even if body composition looks similar externally. Resistance training is the most effective tool for preserving BMR with age, as muscle tissue is metabolically active (burns ~6 calories/lb/day at rest versus ~2 calories/lb/day for fat). Each kilogram of additional muscle raises BMR by approximately 13 calories/day — meaningful over years of training.
Activity Multipliers: Honest Self-Assessment Matters
Most people overestimate their activity level, which leads to overeating relative to actual needs. "Lightly active" means 1–3 days of genuine exercise per week — not occasional walks. "Moderately active" requires consistent 3–5 days of exercise at moderate intensity. If you have an office job and exercise 3 times per week for 45 minutes, lightly active (1.375) is likely more accurate than moderately active (1.55). The difference between these two multipliers on a 1,500 BMR is 263 calories/day — 13 kg per year if consistently misapplied.
How to Calculate BMR by Hand: Worked Example
Using the Mifflin-St Jeor equation — the most widely validated BMR formula in current clinical use — for a 35-year-old male, 80 kg, 178 cm tall:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5.
10×80 + 6.25×178 − 5×35 + 5 = 800 + 1,112.5 − 175 + 5 = 1,742.5 calories/day.
Women use the same structure with a different constant: BMR = 10×weight + 6.25×height − 5×age − 161. For a 35-year-old woman at the same weight and height: 800 + 1,112.5 − 175 − 161 = 1,576.5 calories/day — 166 fewer calories than the male result, reflecting the formula's built-in adjustment for typically higher average body-fat percentage and lower average muscle mass at the same weight and height.
Why does BMR represent only the "resting" baseline, not total daily needs?
BMR measures the energy required for basic involuntary functions alone — breathing, circulation, cell repair — assuming complete physical rest, and explicitly excludes digestion, movement, and exercise. It is intentionally the floor of the calculation, not the answer to "how many calories should I eat," which is what a full TDEE (Total Daily Energy Expenditure) figure — BMR multiplied by an activity factor — is for.
Why Is the Mifflin-St Jeor Formula Preferred Over Older Equations?
How does it compare to the older Harris-Benedict equation?
Harris-Benedict, developed in 1919 and revised in 1984, tends to overestimate BMR by roughly 5% for many people compared to modern validation studies. Mifflin-St Jeor, published in 1990 and validated against a larger, more contemporary, more diverse population sample, is now recommended by most dietetic associations as the more accurate default for the general population — the older formula persists mainly in legacy calculators and older textbooks.
How much does BMR actually decline with age?
The formula's −5×age term shows the mechanism directly: BMR declines by roughly 5 calories per year of age at a constant weight and height, primarily reflecting the gradual loss of metabolically active muscle mass over time. A 55-year-old with identical weight and height to the 35-year-old example above has a BMR about 100 calories/day lower — a modest but real effect that resistance training can partly offset by preserving muscle mass.
Why does honest activity-level self-assessment matter more than most people expect?
Multiplying BMR by an inflated activity factor (choosing "very active" when actual activity is moderate) is one of the most common reasons calculated calorie targets fail to produce expected results — a single activity-level tier can shift the total TDEE estimate by 200–400 calories/day, larger than many people's intended weekly deficit.
Frequently Asked Questions
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest just to keep basic functions running. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor — it's how many calories you actually burn per day.
Mifflin-St Jeor is considered the most accurate general BMR formula, validated in multiple studies. It's accurate within ±10% for most adults. Athletes with very high muscle mass may find it slightly underestimates their BMR.
Eating 500 calories below your TDEE creates a 3,500 calorie weekly deficit — approximately 1 pound of fat loss per week. Never go below 1,200 calories (women) or 1,500 calories (men) without medical supervision.
Sources & Methodology
Calculations are based on the most current publicly available data from authoritative government and industry sources: