BMR Calculator

Female BMR equals 655 plus 9.6 times weight plus 1.8 times height minus 4.7 times age
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How It Works

BMR (Basal Metabolic Rate) is the energy your body burns at complete rest — the calories required to keep your heart beating, lungs breathing, and core temperature stable when you're awake, lying still, and have not eaten for 12+ hours. This calculator uses the original Harris-Benedict equations (1919, rounded coefficients) to estimate BMR from weight, height, and age, with separate coefficients for biological sex. Female BMR = 655 + 9.6w + 1.8h − 4.7a; Male BMR = 66 + 13.7w + 5h − 6.8a, where w is weight in kg, h is height in cm, and a is age in years. The output is in kilocalories per day. The Roza-Shizgal 1984 revision and Mifflin-St Jeor 1990 equations use different coefficients; see Key Concepts.

Example Problem

A 30-year-old woman is 165 cm tall and weighs 70 kg. What is her basal metabolic rate using the Harris-Benedict equation?

  1. Pick the female equation: BMR = 655 + 9.6w + 1.8h − 4.7a.
  2. Substitute: BMR = 655 + 9.6 × 70 + 1.8 × 165 − 4.7 × 30.
  3. Multiply: 655 + 672 + 297 − 141.
  4. Add and subtract left to right: 655 + 672 = 1327; 1327 + 297 = 1624; 1624 − 141 = 1483.
  5. Result: BMR ≈ 1,483 kcal/day. To estimate daily calorie needs, multiply by an activity factor (sedentary 1.2 → very active 1.9) to get TDEE.

Key Concepts

BMR is distinct from RMR (resting metabolic rate), which is measured under less strict conditions and runs about 10% higher. The Harris-Benedict equation was revised in 1984 (Roza & Shizgal) with slightly different coefficients, and the Mifflin-St Jeor equation (1990) is now considered the most accurate of the prediction equations for the general population — but Harris-Benedict remains widely taught and used. All prediction equations have ±10% error vs. indirect calorimetry; for clinical work, measured RMR is preferred.

Applications

  • Estimating a daily calorie target when paired with an activity factor (TDEE).
  • Bariatric and weight-management programs to set baseline metabolic numbers.
  • Sports nutrition for planning energy intake during training cycles.
  • Clinical nutrition for parenteral feeding calculations.
  • Educational tool for understanding why caloric needs vary by sex, age, and body size.

Common Mistakes

  • Using BMR as a direct daily calorie target. BMR is the resting baseline — actual needs include activity, digestion (thermic effect of food, ~10%), and exercise. Multiply by an activity factor to get TDEE before using for diet planning.
  • Applying the Harris-Benedict equation to children, pregnant women, or people with severe illness. The equations were derived from healthy adults; specialized methods apply to those populations.
  • Assuming the male coefficients work for all 'male assigned at birth' bodies. Hormone therapy, body composition, and individual variability all matter — the equation is an estimate.
  • Confusing BMR with metabolism speed. A higher BMR mostly reflects body size, not how 'fast' your metabolism is.
  • Mixing units — entering height in inches but selecting cm in the dropdown will produce wildly wrong numbers. The calculator converts internally if both selectors are set correctly.

Frequently Asked Questions

How do you calculate BMR?

Use the Harris-Benedict equation: Female BMR = 655 + 9.6w + 1.8h − 4.7a; Male BMR = 66 + 13.7w + 5h − 6.8a, where w is weight in kg, h is height in cm, and a is age in years. Result is in kilocalories per day.

What is the formula for BMR?

The Harris-Benedict (1919) formula is sex-specific. For women: BMR = 655 + 9.6 × weight(kg) + 1.8 × height(cm) − 4.7 × age(years). For men: BMR = 66 + 13.7 × weight(kg) + 5 × height(cm) − 6.8 × age(years).

What's the difference between BMR and RMR?

BMR is measured under strict laboratory conditions (12-hour fast, fully rested, neutral temperature). RMR (Resting Metabolic Rate) is measured under less strict conditions and is typically 10% higher than BMR. For everyday calorie estimation, the terms are often used interchangeably.

Is Harris-Benedict the most accurate BMR equation?

No — the Mifflin-St Jeor equation (1990) is now considered slightly more accurate for the general population. Harris-Benedict remains widely used and produces results within ±10% of measured RMR for most healthy adults.

Why does BMR decrease with age?

Two reasons: lean muscle mass tends to decline with age (sarcopenia), and metabolic processes in remaining tissue slow modestly. The Harris-Benedict equation captures the age effect with a linear coefficient (−4.7 for women, −6.8 for men), which is a simplification but matches population averages reasonably well.

How do I use BMR to set a calorie target?

BMR is the resting baseline. To get daily calorie needs (TDEE), multiply by an activity factor: sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, extra active 1.9. To lose weight, eat ~500 kcal below TDEE per day (≈1 lb/week deficit). To gain, add 200–500 kcal above TDEE.

Reference:

This calculator uses the original Harris-Benedict equations (rounded coefficients). Harris JA, Benedict FG. A Biometric Study of Human Basal Metabolism. Proc Natl Acad Sci U S A. 1918;4(12):370-373. https://doi.org/10.1073/pnas.4.12.370

Worked Examples

Endurance Athletics

What is the BMR of a female marathon runner in training?

A 35-year-old female marathon runner is 168 cm tall and weighs 58 kg during a peak training block. What is her resting energy baseline before activity multipliers?

  • Knowns: sex = female, weight w = 58 kg, height h = 168 cm, age a = 35 years.
  • Apply the female Harris-Benedict formula: BMR = 655 + 9.6w + 1.8h − 4.7a.
  • Substitute: BMR = 655 + 9.6 × 58 + 1.8 × 168 − 4.7 × 35.
  • Simplify each term: 655 + 556.8 + 302.4 − 164.5.
  • Sum: 655 + 556.8 + 302.4 = 1,514.2; 1,514.2 − 164.5 = 1,349.7.

BMR ≈ 1,350 kcal/day at rest

On heavy training days a marathon runner may burn 1,500–3,000 additional kcal through running alone — TDEE rises well above BMR. Use the TDEE calculator to apply a very-active activity factor (1.725) on top of this resting baseline.

Military Fitness

How many calories does a 24-year-old male recruit burn at rest?

A 24-year-old male military recruit is 180 cm tall and weighs 80 kg at the start of basic training. What is his Harris-Benedict BMR for nutrition planning?

  • Knowns: sex = male, weight w = 80 kg, height h = 180 cm, age a = 24 years.
  • Apply the male Harris-Benedict formula: BMR = 66 + 13.7w + 5h − 6.8a.
  • Substitute: BMR = 66 + 13.7 × 80 + 5 × 180 − 6.8 × 24.
  • Simplify each term: 66 + 1,096 + 900 − 163.2.
  • Sum: 66 + 1,096 + 900 = 2,062; 2,062 − 163.2 = 1,898.8.

BMR ≈ 1,899 kcal/day at rest

Military training programs typically use an activity factor between 1.725 (very active) and 1.9 (extra active) to plan field rations. Multiply this BMR by 1.9 for an estimated 3,608 kcal/day during peak training.

Geriatric Health

What is the BMR of a 68-year-old active retiree?

A 68-year-old active retired woman is 160 cm tall and weighs 65 kg. Estimate her resting metabolic baseline so a dietitian can set her daily calorie target.

  • Knowns: sex = female, weight w = 65 kg, height h = 160 cm, age a = 68 years.
  • Apply the female Harris-Benedict formula: BMR = 655 + 9.6w + 1.8h − 4.7a.
  • Substitute: BMR = 655 + 9.6 × 65 + 1.8 × 160 − 4.7 × 68.
  • Simplify each term: 655 + 624 + 288 − 319.6.
  • Sum: 655 + 624 + 288 = 1,567; 1,567 − 319.6 = 1,247.4.

BMR ≈ 1,247 kcal/day at rest

Informational only — not a substitute for clinical judgment. Harris-Benedict was derived on younger adults; in older adults the equation tends to slightly overestimate BMR because lean mass declines with age. Mifflin-St Jeor or DEXA-derived lean mass gives a closer estimate.

BMR Formulas (Harris-Benedict)

Basal Metabolic Rate (BMR) is the energy your body burns at rest to maintain core processes — breathing, circulation, cell turnover, body-temperature regulation. This calculator uses the original Harris-Benedict equations (1919), which estimate BMR in kilocalories per day from weight, height, age, and biological sex:

BMR = 66 + 13.7w + 5h − 6.8aMen (Harris-Benedict)
BMR = 655 + 9.6w + 1.8h − 4.7aWomen (Harris-Benedict)

Where:

  • BMR — basal metabolic rate in kilocalories per day (kcal/day)
  • w — body weight in kilograms (kg)
  • h — standing height in centimeters (cm)
  • a — age in years

The original 1919 Harris-Benedict equations tend to over-estimate modern BMR by roughly 5%, partly because body composition reference ranges have shifted since the early 20th century. The Mifflin-St Jeor equation (1990) is now generally considered more accurate for contemporary adults, but Harris-Benedict remains widely cited in textbooks and fitness literature. BMR is the metabolic baseline only — to estimate full daily calorie needs, multiply BMR by an activity factor (use the TDEE calculator). Neither equation accounts for differences in lean body mass, thyroid function, or medications. This calculator is informational only and is not a substitute for clinical judgment.

Daily Calorie Needs by Activity Level

BMR is your resting baseline. To estimate the calories you actually burn in a day, multiply BMR by an activity factor — this gives your Total Daily Energy Expenditure (TDEE). The table below applies each Harris-Benedict activity factor to your computed BMR. For full daily-calorie planning with activity-level definitions, use the TDEE calculator.

Activity LevelFactorEst. Daily Calories
Sedentarylittle or no exercise, desk job×1.2—
Lightly activelight exercise 1–3 days/week×1.375—
Moderately activemoderate exercise 3–5 days/week×1.55—
Very activehard exercise 6–7 days/week×1.725—
Extra activevery hard exercise or physical job×1.9—

Estimated daily calories = BMR × activity factor (Harris-Benedict). These are starting estimates for maintenance; actual needs vary with body composition, NEAT, and individual metabolism.

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