{
  "slug": "bmr-mifflin",
  "title": "BMR Calculator (Mifflin-St Jeor)",
  "category": "Body Composition",
  "category_slug": "body-composition",
  "tier": 1,
  "summary": "Estimate daily resting energy expenditure using the Mifflin-St Jeor equation for males and females.",
  "description": "This calculator estimates Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, a widely validated formula published in 1990. It takes weight in kilograms, height in centimeters, age in years, and biological sex as inputs, then returns an estimate of daily resting energy expenditure in kilocalories. The equation was derived from indirect calorimetry studies in adult populations and is considered one of the most accurate prediction methods for healthy individuals.",
  "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmr-mifflin/",
  "api_url": "https://fitmetriclab.com/api/tools/bmr-mifflin.json",
  "formula": {
    "id": "bmr_mifflin",
    "expression": "\\text{BMR} = \\begin{cases} 10w + 6.25h - 5a + 5 & \\text{male} \\\\ 10w + 6.25h - 5a - 161 & \\text{female} \\end{cases}",
    "variables": [
      {
        "symbol": "w",
        "description": "Weight in kg"
      },
      {
        "symbol": "h",
        "description": "Height in cm"
      },
      {
        "symbol": "a",
        "description": "Age in years"
      },
      {
        "symbol": "s",
        "description": "Sex (male/female)"
      }
    ]
  },
  "inputs": [
    {
      "id": "weight_kg",
      "label": "Weight",
      "type": "number",
      "unit": "kg",
      "default": 75,
      "min": 20,
      "max": 300,
      "step": 0.1
    },
    {
      "id": "height_cm",
      "label": "Height",
      "type": "number",
      "unit": "cm",
      "default": 175,
      "min": 100,
      "max": 230,
      "step": 0.5
    },
    {
      "id": "age",
      "label": "Age",
      "type": "number",
      "unit": "years",
      "default": 30,
      "min": 10,
      "max": 100,
      "step": 1
    },
    {
      "id": "sex",
      "label": "Sex",
      "type": "select",
      "unit": null,
      "default": 1,
      "options": [
        {
          "label": "Male",
          "value": 1
        },
        {
          "label": "Female",
          "value": 0
        }
      ]
    }
  ],
  "worked_example": {
    "inputs": {
      "weight_kg": 75,
      "height_cm": 175,
      "age": 30,
      "sex": 1
    },
    "expected_output": "1,699 kcal"
  },
  "result_summary_template": "For an individual weighing {weight_kg} kg, standing {height_cm} cm tall, aged {age} years, the Mifflin-St Jeor equation estimates basal metabolic rate at {result}.",
  "methodology": "Applies the Mifflin-St Jeor equation (1990): males = 10w + 6.25h − 5a + 5; females = 10w + 6.25h − 5a − 161, where w = weight (kg), h = height (cm), a = age (years). Derived from indirect calorimetry studies and validated against measured resting metabolic rate in adult populations.",
  "sources": [
    {
      "label": "Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-7.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/2305711/"
    },
    {
      "label": "Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-89.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/15883556/"
    },
    {
      "label": "Academy of Nutrition and Dietetics. Resting Metabolic Rate Measurement and Prediction Equations. Evidence Analysis Library.",
      "url": "https://www.andeal.org/"
    }
  ],
  "faqs": [
    {
      "question": "What is the difference between BMR and TDEE?",
      "answer": "BMR (Basal Metabolic Rate) represents the calories required at complete rest for basic physiological functions. TDEE (Total Daily Energy Expenditure) includes BMR plus all activity—exercise, non-exercise movement, and the thermic effect of food. This calculator estimates BMR only; activity multipliers are applied separately to estimate TDEE."
    },
    {
      "question": "Why does the Mifflin-St Jeor equation use different constants for males and females?",
      "answer": "The +5 constant for males and −161 for females reflect population-average differences in lean body mass, hormonal profiles, and body composition. Males typically carry more skeletal muscle and less essential body fat, resulting in higher resting energy expenditure per unit of body weight when other variables are held constant."
    },
    {
      "question": "How accurate is the Mifflin-St Jeor equation compared to measured BMR?",
      "answer": "Validation studies show the Mifflin-St Jeor equation predicts measured resting metabolic rate within approximately ±10% for most individuals in the general population. Individual error can be larger due to genetic variation, thyroid function, medication use, and body-composition extremes not captured by weight, height, age, and sex alone."
    },
    {
      "question": "Can I use this calculator if I am very muscular or very lean?",
      "answer": "The equation does not account for body composition directly—only total weight. Individuals with significantly above-average lean mass (competitive bodybuilders, strength athletes) or below-average body fat (elite endurance athletes, physique competitors) may find the prediction underestimates or overestimates true BMR because muscle tissue is more metabolically active than adipose tissue."
    },
    {
      "question": "Why does BMR decrease with age in the formula?",
      "answer": "The −5 coefficient for age reflects the observed decline in resting metabolic rate as people age, primarily due to loss of lean tissue and changes in cellular metabolism. The equation subtracts 5 calories per year of age, meaning a 50-year-old has a predicted BMR 100 kcal/day lower than a 30-year-old with identical weight, height, and sex."
    }
  ],
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    {
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      "title": "BMI Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/bmi-calculator.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmi-calculator/"
    },
    {
      "slug": "tdee-calculator",
      "title": "TDEE Calculator",
      "api_url": "https://fitmetriclab.com/api/tools/tdee-calculator.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/tdee-calculator/"
    },
    {
      "slug": "bmr-harris-benedict",
      "title": "BMR Calculator (Harris-Benedict)",
      "api_url": "https://fitmetriclab.com/api/tools/bmr-harris-benedict.json",
      "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmr-harris-benedict/"
    }
  ],
  "last_updated": "2026-04-22",
  "price": {
    "value": 0,
    "currency": "USD"
  },
  "runs_in_browser": true,
  "disclaimer": "Educational estimate produced from a published formula. Not medical, nutritional, or training advice. Calculations are deterministic — apply the formula to the inputs to reproduce the result."
}