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BMR

General

Basal Metabolic Rate

The number of calories your body burns at complete rest to maintain basic functions — breathing, circulation, cell repair — forming the baseline for all calorie and diet planning.

Definition

BMR (Basal Metabolic Rate) is the number of calories your body needs to perform its most essential functions — breathing, circulation, cell production, and organ function — while completely at rest. It represents the minimum energy requirement to sustain life, measured under strict resting conditions (fasted, lying down, after a full night's sleep).

BMR is the foundation of all caloric calculations. Understanding your BMR allows you to:

  • Calculate your Total Daily Energy Expenditure (TDEE) by adjusting for activity level
  • Set appropriate caloric intake targets for weight loss, maintenance, or gain
  • Understand why dieting becomes harder over time (metabolic adaptation)
  • Make informed decisions about nutrition and exercise interventions

BMR is influenced by: age, gender, height, weight, body composition (muscle-to-fat ratio), hormonal health, and genetic factors. Among these, body composition (specifically muscle mass) is the most actionable lever for increasing BMR.

Formula

Mifflin-St Jeor Equation (recommended):

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161

Harris-Benedict Equation (original, widely used):

Men: BMR = 88.362 + (13.397 × weight kg) + (4.799 × height cm) − (5.677 × age)

Women: BMR = 447.593 + (9.247 × weight kg) + (3.098 × height cm) − (4.330 × age)

TDEE from BMR:

TDEE = BMR × Activity Multiplier (see TDEE entry for multipliers)

Worked Example

Priya: Female, 30 years old, 62 kg, 162 cm height

Mifflin-St Jeor: BMR = (10 × 62) + (6.25 × 162) − (5 × 30) − 161 = 620 + 1,012.5 − 150 − 161 = 1,321.5 kcal/day

Interpretation: Priya's body burns approximately 1,322 calories per day simply to survive — before any physical activity, digestion, or other energy expenditure is added.

TDEE estimate (if Priya is lightly active, 1–3 days/week exercise): TDEE = 1,321.5 × 1.375 = 1,817 kcal/day

For 0.5 kg/week weight loss (500 kcal/day deficit): Target daily calories = 1,817 − 500 = 1,317 kcal/day

Use the BMR calculator to get your personalised BMR and the TDEE calculator for your maintenance calories.

Key Things to Know

  • BMR ≠ actual minimum safe eating: BMR is the energy for vital functions at complete rest — the body still needs additional calories for digestion (thermic effect of food, ~10% of calories), even light movement, and normal daily activity. Eating at BMR level (i.e., eating only your BMR calories) creates a deficit equivalent to your activity and thermic effect. Eating below BMR for extended periods risks nutrient deficiencies and triggers metabolic adaptation — not recommended without medical supervision.
  • Muscle mass is the BMR multiplier: Fat tissue burns approximately 2 kcal/kg/day at rest; muscle tissue burns approximately 13 kcal/kg/day. This means adding 5 kg of muscle increases BMR by approximately 55 kcal/day — equivalent to a 20-minute walk. Resistance training is the only evidence-backed way to meaningfully raise BMR beyond caloric intake and basic lifestyle factors.
  • Thyroid function and BMR: The thyroid gland produces hormones (T3, T4) that directly regulate metabolic rate. Hypothyroidism (underactive thyroid) reduces BMR — people with hypothyroidism can maintain or gain weight despite caloric restriction. Hyperthyroidism increases BMR — people can lose weight despite adequate intake. Unexplained BMR divergence from formula estimates warrants thyroid function testing.
  • BMR after weight loss: As you lose weight, BMR decreases because: (1) you're carrying less mass (fewer calories needed to maintain), and (2) metabolic adaptation (the body becomes more efficient). After significant weight loss, recalculate BMR and TDEE at your new weight. Expecting to maintain the same caloric deficit that achieved weight loss is the most common reason for weight loss plateaus.
  • BMI vs BMR — two different tools: BMI tells you about body composition relative to population norms. BMR tells you how many calories your body burns at rest. A muscular athlete may have a "high" BMI but also a high BMR. BMR is a metabolic rate indicator, not a health indicator — the two are independent measures that serve different purposes.

Related Calculators

BMR Calculator →Calculate your Basal Metabolic Rate using the Mifflin-St Jeor equation. Know your minimum daily calorie need to maintain basic body functions at rest.
TDEE Calculator →Calculate your Total Daily Energy Expenditure (TDEE) based on your BMR and activity level. Find your maintenance calories for weight loss or muscle gain.
Calorie Calculator →Calculate daily calorie needs from age, weight, and activity level. Get targets for weight loss, maintenance, or muscle gain with macros and hydration guidance.

Related Terms

BMIBody Mass IndexTDEETotal Daily Energy Expenditure
Frequently Asked Questions
Which BMR formula is most accurate — Mifflin-St Jeor or Harris-Benedict?
The Mifflin-St Jeor equation (1990) is considered more accurate than the original Harris-Benedict equation (1919) for most modern adults. A 2005 study in the Journal of the American Dietetic Association found Mifflin-St Jeor predicted RMR within 10% for 82% of subjects vs 81% for Harris-Benedict. However, Harris-Benedict was updated in 1984 and the revised version is nearly as accurate as Mifflin-St Jeor. For most practical purposes (caloric planning with ±200 kcal accuracy), both provide adequate estimates. Mifflin-St Jeor is the formula used by most dietitians today.
How does age affect BMR?
BMR declines approximately 1–2% per decade after age 20, primarily due to loss of lean muscle mass (sarcopenia). Men typically lose 3–5% of muscle mass per decade after 30. A 60-year-old may have 15–20% lower BMR than they did at 25, even at the same body weight. Resistance training (lifting weights) is the most effective intervention to counter age-related BMR decline — building or maintaining muscle mass keeps metabolic rate higher. This is why older adults who strength-train can maintain similar BMR to younger sedentary individuals.
Why is BMR important for weight management?
BMR represents the minimum calories needed just to keep vital functions running. Most adults spend 60–75% of their total daily calorie expenditure on BMR alone. When people drastically reduce calories (crash diets), the body adapts by reducing BMR — a mechanism called metabolic adaptation or 'starvation mode'. This is why very low calorie diets become increasingly ineffective over time. A sustainable caloric deficit of 15–20% below TDEE (which incorporates BMR) promotes fat loss without triggering the metabolic adaptation that makes aggressive dieting counterproductive.
What is the difference between BMR and RMR?
BMR (Basal Metabolic Rate) is technically measured under strict conditions: 12-hour fast, completely at rest, lying down, in a thermoneutral environment, having slept 8 hours. RMR (Resting Metabolic Rate) is measured at rest but without the strict 12-hour fast requirement — more practical to measure clinically. RMR is typically 10–20% higher than BMR because of the thermic effect of recent food. The terms are often used interchangeably in nutrition practice, but technically RMR is the more commonly measured value in clinical settings.
Can you increase your BMR?
Yes. Since muscle tissue burns more calories at rest than fat tissue, building muscle increases BMR. Strategies: (1) Resistance training — the most evidence-backed approach; each kg of added muscle raises BMR by approximately 13 kcal/day. (2) High-protein diet — protein has the highest thermic effect of food (25–30% of calories consumed) and preserves muscle during weight loss. (3) Adequate sleep — sleep deprivation reduces metabolism and increases hunger hormones. (4) Avoid prolonged very-low-calorie diets — they trigger BMR reduction.