BMR Calculator

Your body burns calories even when you’re sleeping. Understanding how many calories you burn at rest–your basal metabolic rate (BMR)–is the foundation for any weight loss, muscle-building, or nutrition plan.

What Is Basal Metabolic Rate (BMR)?

Basal metabolic rate is the number of calories your body burns each day at rest to maintain basic functions: breathing, circulation, cell production, nutrient processing, and temperature regulation. It’s the minimum energy your body requires to survive without any physical activity.

Your BMR accounts for 60–75% of your total daily calorie expenditure in a sedentary person. This is why understanding it matters: it shows you exactly how much you can eat without gaining weight, even on days you don’t exercise.

BMR is different from resting metabolic rate (RMR). RMR is similar but measured under less strict conditions. For practical purposes, the terms are used interchangeably, and calculators treat them the same way.

How Is BMR Calculated?

The most accurate formula used today is the Mifflin-St Jeor equation (1990). It accounts for age, weight, height, and sex:

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

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

The earlier Harris-Benedict equation (1919) is less accurate but still used:

For men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)

For women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)

For people who know their body fat percentage, the Katch-McArdle formula is most precise: BMR = 370 + (21.6 × lean body mass in kg)

The calculator above uses the Mifflin-St Jeor equation, which is the standard recommended by most nutritionists and fitness professionals.

Factors That Affect Your BMR

Your BMR isn’t static. Several factors influence how many calories your body burns at rest:

Muscle mass – Muscle tissue is metabolically active and burns more calories than fat. People with more muscle have higher BMRs. This is why resistance training effectively increases your metabolism.

Age – BMR decreases approximately 2–8% per decade after age 30 due to natural muscle loss, unless you actively prevent it through strength training.

Sex – Men typically have higher BMRs than women because they naturally have more muscle mass. Women also have higher body fat percentages on average.

Body composition – Two people weighing the same but with different muscle-to-fat ratios will have different BMRs. The person with more muscle burns more calories.

Genetics – Some people inherit a naturally faster or slower metabolism. This accounts for 20–30% variation in BMR between individuals.

Hormones – Thyroid hormones directly regulate metabolism. Conditions like hypothyroidism lower BMR, while hyperthyroidism raises it. Hormonal fluctuations also affect women’s BMR throughout the menstrual cycle.

Temperature regulation – Living in a cold climate requires more energy to maintain body temperature, slightly raising BMR. Chronic stress and poor sleep lower metabolic rate.

How to Use Your BMR for Weight Loss and Fitness

Knowing your BMR is the starting point; your total calorie needs depend on your activity level. Multiply your BMR by an activity factor:

• Sedentary (little or no exercise): BMR × 1.2
• Lightly active (1–3 days exercise/week): BMR × 1.375
• Moderately active (3–5 days exercise/week): BMR × 1.55
• Very active (6–7 days exercise/week): BMR × 1.725
• Extremely active (physical job, training twice daily): BMR × 1.9

This gives you your TDEE (Total Daily Energy Expenditure).

For weight loss: Consume 300–500 calories below your TDEE. A 500-calorie deficit typically results in losing 0.5 kg (1 lb) per week.

For weight maintenance: Eat at your TDEE.

For muscle gain: Consume 300–500 calories above your TDEE while doing strength training.

Never eat below your BMR for extended periods. Your body needs those baseline calories to function, and extreme undereating slows metabolism and causes muscle loss.

BMR vs. TDEE: What’s the Difference?

BMR is calories burned at complete rest. TDEE includes BMR plus:

• Calories from daily activities (walking, work, household tasks)
• Calories from structured exercise
• Thermic effect of food (energy to digest)

Your TDEE is always higher than your BMR. If your BMR is 1,500 calories and you’re moderately active, your TDEE might be around 2,325 calories. That’s the number you should use to set your eating targets.

Why BMR Matters for Your Goals

Understanding your BMR removes guesswork from nutrition planning. Instead of following generic “eat 2,000 calories” advice, you have a personalized baseline. You know exactly how much you can eat to lose, maintain, or gain weight.

It also explains why two people following the same diet have different results–they have different BMRs. A 5'4" woman and a 5'10" man will burn completely different amounts at rest.

This calculator provides estimates based on research-backed formulas. Individual metabolic rates vary, and for medical concerns about metabolism, consult a healthcare provider or registered dietitian.