{
  "slug": "bmr-harris-benedict",
  "title": "BMR Calculator (Harris-Benedict)",
  "category": "Body Composition",
  "category_slug": "body-composition",
  "tier": 2,
  "summary": "Estimate basal metabolic rate using the 1984 revised Harris-Benedict equation.",
  "description": "This calculator estimates basal metabolic rate (BMR) using the 1984 revised Harris-Benedict equation published by Roza and Shizgal. It requires weight, height, age, and biological sex as inputs, then applies sex-specific formulas to estimate daily resting energy expenditure in kilocalories. The equation was derived from studies of healthy adults and provides a population-average estimate of the calories the body burns at complete rest to maintain vital functions.",
  "page_url": "https://fitmetriclab.com/en/tools/body-composition/bmr-harris-benedict/",
  "api_url": "https://fitmetriclab.com/api/tools/bmr-harris-benedict.json",
  "formula": {
    "id": "bmr_harris_benedict",
    "expression": "\\text{BMR} = \\begin{cases} 13.397w + 4.799h - 5.677a + 88.362 & \\text{male} \\\\ 9.247w + 3.098h - 4.330a + 447.593 & \\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": "yrs",
      "default": 30,
      "min": 10,
      "max": 100,
      "step": 1
    },
    {
      "id": "sex",
      "label": "Sex",
      "type": "select",
      "unit": null,
      "default": 1,
      "options": [
        {
          "value": 1,
          "label": "Male"
        },
        {
          "value": 0,
          "label": "Female"
        }
      ]
    }
  ],
  "worked_example": {
    "inputs": {
      "weight_kg": 75,
      "height_cm": 175,
      "age": 30,
      "sex": 1
    },
    "expected_output": "1,763 kcal"
  },
  "result_summary_template": "For an individual weighing {weight_kg} kg at {height_cm} cm tall and {age} years of age, the revised Harris-Benedict equation estimates basal metabolic rate at {result}.",
  "methodology": "Applies the 1984 revised Harris-Benedict equations (Roza & Shizgal, Am J Clin Nutr 1984). Males: 88.362 + 13.397×weight_kg + 4.799×height_cm − 5.677×age. Females: 447.593 + 9.247×weight_kg + 3.098×height_cm − 4.330×age. Estimates basal metabolic rate from anthropometric data.",
  "sources": [
    {
      "label": "Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-82.",
      "url": "https://pubmed.ncbi.nlm.nih.gov/6741850/"
    },
    {
      "label": "Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism. Proc Natl Acad Sci U S A. 1918;4(12):370-3.",
      "url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1091498/"
    },
    {
      "label": "Frankenfield D, et al. 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/"
    }
  ],
  "faqs": [
    {
      "question": "What is the difference between the original and revised Harris-Benedict equations?",
      "answer": "The original Harris-Benedict equations were published in 1919 based on indirect calorimetry of 136 men, 103 women, and 94 children. The 1984 revision by Roza and Shizgal recalculated the coefficients using updated data and statistical methods, resulting in different intercept and slope constants for both male and female formulas."
    },
    {
      "question": "Why does BMR decline with age in the formula?",
      "answer": "The negative age coefficient reflects the population-level trend of declining lean body mass and reduced cellular metabolic activity with advancing age. The equation incorporates a fixed age penalty of approximately 5.7 kcal/day per year for males and 4.3 kcal/day per year for females, derived from cross-sectional regression analysis."
    },
    {
      "question": "How does this differ from the Mifflin-St Jeor equation?",
      "answer": "The Mifflin-St Jeor equation was published in 1990 using a larger, more contemporary sample. It typically produces estimates 5–10% lower than Harris-Benedict for the same inputs. Both are population-derived linear models; neither directly measures individual metabolic rate."
    },
    {
      "question": "Can this estimate be used for total daily energy expenditure?",
      "answer": "No. BMR represents resting metabolism only. Total daily energy expenditure requires multiplying BMR by an activity factor (often 1.2 to 2.0) to account for physical activity, the thermic effect of food, and non-exercise activity thermogenesis. This calculator returns only the basal component."
    },
    {
      "question": "What measurement conditions does the equation assume?",
      "answer": "The Harris-Benedict equations assume standard indirect calorimetry conditions: post-absorptive state (8–12 hours fasted), supine rest, thermoneutral environment, and absence of acute illness or psychological stress. Real-world measurements taken under different conditions may deviate from the estimate."
    }
  ],
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  "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."
}