BMR Calculator
Your Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest to sustain basic life functions. This calculator uses both the Mifflin-St Jeor and Harris-Benedict equations.
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Formula
BMR (Mifflin) = 10W + 6.25H − 5A + S
W = weight in kg, H = height in cm, A = age in years, S = +5 for males and −161 for females. The Harris-Benedict equation uses different coefficients and produces slightly different results. Mifflin-St Jeor is generally considered more accurate for modern populations.
How to use the BMR Calculator
- 1
Enter your weight
Value should be in kg.
- 2
Enter your height
Value should be in cm.
- 3
Enter your age
Value should be in years.
- 4
Enter your sex
- 5
Read your results instantly
Results update in real time as you type.
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What BMR represents
Imagine being in a medically induced coma — no movement, no digestion, no stress response. The calories your body burns just to keep organs functioning, maintain body temperature, pump blood, and breathe is your BMR. It represents 60–75% of most people's total daily energy expenditure.
BMR is primarily driven by lean muscle mass (which is metabolically active) and body size. This is why building muscle increases long-term calorie burn even at rest.
Mifflin-St Jeor vs. Harris-Benedict
The Harris-Benedict equation was developed in 1919 and revised in 1984. The Mifflin-St Jeor equation was developed in 1990 using a more modern population sample. Multiple validation studies have found Mifflin-St Jeor to be more accurate for most adults, predicting calorie needs within 10% for about 82% of subjects.
Harris-Benedict tends to overestimate by about 5% on average. Both are reasonable starting points — track your actual weight response to calibrate.
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Factors that influence BMR
Age is the most consistent factor — BMR declines roughly 1–2% per decade after age 20, primarily due to muscle loss. Sex matters too: men generally have higher BMR due to greater muscle mass.
Other factors: thyroid function (hyperthyroidism raises BMR dramatically), temperature (cold climates slightly elevate BMR), nutritional status (severe restriction lowers BMR through metabolic adaptation), and muscle mass (each kg of muscle burns approximately 13 calories/day at rest).
Tips & Insights
BMR is your floor, not your target
Never eat below your BMR for extended periods. This forces the body to break down muscle for energy, lowering future metabolic rate and making weight management harder long-term.
Resistance training raises resting metabolism
Adding 5kg of muscle increases resting calorie burn by ~65 calories/day — about 23,000 calories per year, or roughly 3kg of fat without changing diet.
Worked Examples
30-year-old woman
Mifflin BMR: ~1,419 cal/day. Harris-Benedict BMR: ~1,468 cal/day. To get TDEE, multiply by activity factor (e.g., 1.375 for lightly active = ~1,950–2,018 cal/day).
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Frequently Asked Questions
How accurate is BMR?
The Mifflin-St Jeor equation is considered the most accurate for most people, with an error rate of about 10%. Individual variations in metabolism, thyroid function, and muscle mass can affect accuracy.
Should I eat my BMR calories?
BMR is the minimum calories to sustain basic functions at complete rest. Since you're not comatose, your actual needs (TDEE) are higher. Eating only your BMR while active creates a large deficit.
Can I increase my BMR?
Yes — primarily through building muscle mass via resistance training. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. Adequate sleep and thyroid health also influence BMR.
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