🔥 BMR Calculator

What is Basal Metabolic Rate (BMR)?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns per day to sustain essential biological functions while at complete rest — with no food consumed and no physical activity performed. This includes breathing, circulating blood, regulating body temperature, growing and repairing cells, and maintaining organ function. Think of it as your body's baseline "idle" energy consumption, similar to a car's fuel consumption at a standstill with the engine running.

BMR is a foundational number in nutrition science. All daily calorie recommendations start from BMR and build upward by adding activity-related energy expenditure. For most adults, BMR accounts for 60–75% of total daily calorie burn — making it by far the largest component of your energy needs, even if you exercise regularly.

The Two BMR Equations

This calculator shows results from both widely used BMR equations:

• Mifflin-St Jeor (1990):
  • Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
  • Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
  Validated in multiple studies as the most accurate for most adults. Recommended by the Academy of Nutrition and Dietetics as the preferred equation for non-obese individuals.
• Harris-Benedict (revised 1984):
  • Men: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
  • Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)
  The original was developed in 1919, revised in 1984. Still widely used, especially in clinical settings. Tends to slightly overestimate BMR compared to Mifflin-St Jeor.

For most purposes, Mifflin-St Jeor is the better choice. If you're significantly overweight or obese, the Katch-McArdle formula (which accounts for lean body mass) may be more accurate, though it requires a body fat percentage measurement.

The Three Components of Total Daily Energy Expenditure (TDEE)

• BMR (60–75%): The largest component. Determined primarily by your body composition (muscle mass burns more than fat at rest), age (BMR declines ~2% per decade after 30), and gender.
• Physical Activity (15–30%): Both intentional exercise and incidental movement (NEAT — Non-Exercise Activity Thermogenesis). NEAT includes walking, fidgeting, standing, and all movement outside formal exercise. NEAT varies enormously between individuals — up to 2,000 calories/day difference — and is a major factor in why people gain weight in sedentary jobs.
• Thermic Effect of Food (8–10%): The energy required to digest, absorb, and metabolize food. Protein has the highest thermic effect (20–30% of protein calories are burned in processing), followed by carbohydrates (5–10%), and fat (0–3%).

Factors That Affect Your BMR

• Muscle mass: The biggest controllable factor. Skeletal muscle burns approximately 6–10 calories per pound per day at rest. Resistance training increases muscle mass and raises BMR permanently.
• Age: BMR declines with age due to muscle loss (sarcopenia) and hormonal changes. Strength training can slow or partially reverse this decline.
• Thyroid function: Hypothyroidism reduces BMR; hyperthyroidism increases it. If your calorie intake seems very low but you're not losing weight, thyroid function is worth checking with a doctor.
• Body temperature and climate: Living in cold environments slightly increases BMR as the body works to maintain core temperature.
• Caloric restriction: Sustained calorie deficits reduce BMR by 15–20% (adaptive thermogenesis) — the body's survival mechanism that makes prolonged dieting progressively harder.

Frequently Asked Questions

How do I use my BMR to lose weight? Multiply your BMR by an activity factor (1.2 for sedentary to 1.9 for very active) to get your TDEE. Eating 500 calories below your TDEE creates a weekly deficit equivalent to roughly 1 pound of fat. Don't eat below your BMR for extended periods — it risks muscle loss and metabolic adaptation.

Can I increase my BMR? Yes. Building muscle through resistance training is the most effective long-term strategy — more muscle means higher resting calorie burn. Adequate sleep, managing stress (high cortisol is associated with lower BMR), and avoiding very low calorie diets all help maintain or improve metabolic rate.

Why is my BMR different from what I calculated before? Small differences between calculators are normal and result from using different formulas. Your actual BMR can only be precisely measured using laboratory equipment (indirect calorimetry). Online calculators are estimates with inherent variability of ±10–15%.