BMR (Basal Metabolic Rate) is the number of calories your body needs to sustain basic life functions — breathing, circulation, organ function, and cell repair — while at complete rest. It represents 60–75% of total daily energy expenditure for most people.

What is the difference between BMR and TDEE?

BMR is your calorie burn at complete rest. TDEE (Total Daily Energy Expenditure) is your total daily calorie burn including all physical activity, exercise, and the thermic effect of food. TDEE = BMR × Activity Multiplier.

Which BMR formula is most accurate?

For most people, the Mifflin-St Jeor formula is the most accurate. If you know your body fat percentage, the Katch-McArdle formula is more precise because it uses lean body mass directly. The original Harris-Benedict formula tends to slightly overestimate BMR.

How do I use my BMR to lose weight?

To lose weight, eat fewer calories than your TDEE (not your BMR). A deficit of 500 kcal/day below TDEE leads to approximately 0.45 kg (1 lb) of fat loss per week. Never eat below your BMR for extended periods — it can harm metabolism and lean mass.

Does BMR decrease with age?

Yes. BMR typically declines by about 1–2% per decade after age 20, primarily due to loss of metabolically active lean muscle mass. Resistance training is the most effective way to maintain or increase BMR as you age.

What factors increase BMR?

BMR is increased by: more lean muscle mass, being male (due to higher average muscle mass), taller stature, being younger, fever or illness, certain hormones (thyroid hormones, adrenaline), cold environments, and pregnancy.

What is the Katch-McArdle formula?

The Katch-McArdle formula calculates BMR directly from lean body mass (LBM): BMR = 370 + (21.6 × LBM in kg). Because it uses LBM instead of total weight, it's considered the most accurate formula for people who know their body fat percentage.

Should I eat at my BMR to lose weight?

No. You should eat at or slightly below your TDEE (not BMR) to lose weight safely. Consistently eating at or below BMR can trigger adaptive thermogenesis, where your metabolism slows down to compensate, making long-term weight loss harder.

Free BMR Calculator — Basal Metabolic Rate, TDEE & Calorie Goal

📝 Your Details

Fill in the required fields for your personalized BMR. Body fat % is optional but unlocks the Katch-McArdle formula.

Unit System

Biological Sex (used in BMR formula)

Age (years, required)

Please enter a valid age (15–90).

Height (cm)

Please enter a valid height (120–220 cm).

Weight (kg)

Please enter a valid weight (35–300 kg).

Body Fat % (optional — unlocks Katch-McArdle formula)

If provided, the Katch-McArdle formula becomes available — the most accurate BMR method.

Please enter a valid body fat % (3–65%).

Activity Level

Please select your activity level.

Your Primary Goal

Please select your goal.

BMR Formula (which calculation to use)

Auto uses Katch-McArdle if body fat % is entered, otherwise Mifflin-St Jeor.

Your Metabolic Profile

Results update live as you fill in your details.

👈 Fill in your details to see your BMR

Required: age, height, weight, activity level, goal.

🧬 Your Basal Metabolic Rate Formula: —

—kcal/day

This is the energy your body burns at complete rest — just to keep organs functioning.

BMR per kg of body weight—

BMR per hour—

Metabolic Category—

⚡ TDEE & Activity Breakdown Activity: —

—kcal/day (your TDEE)

Your Total Daily Energy Expenditure at your selected activity level. See all levels below.

🔬 Formula Comparison Using: —

See your BMR from all three scientific formulas side by side.

💡 Katch-McArdle requires body fat %. Enter it above to unlock this formula.

🎯 Goal Calorie Planner Goal: —

Daily calorie targets based on your TDEE and each possible goal. Your selected goal is highlighted.

                    Your Target
                    —
                  

Estimated weekly weight change —

🔍 Metabolic Insights

Key numbers and context about your metabolism.

🔥 BMR

—

kcal at rest

⚡ TDEE

—

kcal total burn

🏋️ Lean Mass

—

kg lean body mass

📊 BMR %

—

of TDEE at rest

🫀 Where Your BMR Calories Go

Approximate organ contribution to resting energy expenditure.

Liver 27%

Brain 19%

Muscle 18%

Kidney 10%

Heart 7%

Other 19%

Liver

Brain

Skeletal Muscle

Kidneys

Heart

Other Organs

💡 Personalized Metabolic Tips

Research-backed guidance based on your BMR, TDEE, and goal.

BMR: —

⚠️ Disclaimer: BMR and TDEE are estimates based on population-level formulas. Individual metabolic rates vary. These numbers are starting points — adjust based on real-world results after 2–3 weeks of tracking. Not a substitute for medical nutrition advice. If you have a metabolic condition (thyroid disease, PCOS, diabetes), consult a registered dietitian.

🧬 Science-backed metabolic calculations

Know your metabolism — before you count a single calorie

BMR is the foundation of every calorie goal. Without knowing how many calories your body burns at rest, any calorie target you follow is just a guess. This calculator gives you your precise resting energy expenditure using up to three validated scientific formulas — so your calorie goal is built on real data, not population averages.

What Is BMR (Basal Metabolic Rate)?

BMR — Basal Metabolic Rate — is the number of calories your body requires to perform its most basic life-sustaining functions while at complete physical and mental rest. This includes breathing, circulation, maintaining body temperature, cell production, protein synthesis, and the energy demands of every organ.

BMR does not include any physical activity, digestion, or movement. It represents the minimum calorie requirement to simply stay alive — essentially, the calories you'd burn if you stayed in bed all day.

For most sedentary adults, BMR accounts for 60–75% of total daily calorie expenditure. This makes BMR the single most important number in any nutrition or weight management plan.

BMR vs RMR — What's the Difference?

RMR (Resting Metabolic Rate) is often used interchangeably with BMR, but there is a technical distinction. BMR is measured under strict conditions (12-hour fast, complete rest, controlled temperature). RMR is measured under less strict conditions and is typically 10–20% higher than true BMR. Most calculators, including this one, estimate BMR using equations that closely approximate RMR — so both terms are commonly used to refer to the same practical concept.

How to Use This BMR Calculator

Choose unit system: Metric (kg/cm) or Imperial (lbs/ft&in).
Select biological sex: BMR formulas use different constants for males and females due to average body composition differences.
Enter age, height, and weight: All three are required for accurate BMR calculation.
Body fat % (optional but recommended): If you know your body fat percentage, enter it. This unlocks the Katch-McArdle formula — the most accurate method for people who know their lean body mass.
Select activity level: This multiplies your BMR to give your TDEE. Choose the level that best represents your average weekly activity — when in doubt, go lower and adjust after 2 weeks.
Choose your goal: From extreme weight loss to aggressive muscle gain. This adjusts your daily calorie target from your TDEE.
Select formula (optional): Auto mode picks the best formula automatically. Advanced users can manually select Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle.
Read your results: BMR, TDEE at all activity levels, formula comparison, goal calorie planner, metabolic insights, and personalized tips.

The Three BMR Formulas — Explained

This calculator supports three scientifically validated BMR estimation methods. Each has its own strengths depending on your situation.

Mifflin-St Jeor Most Accurate — Recommended

Developed in 1990, the Mifflin-St Jeor equation is widely considered the most accurate BMR formula for the general population. Multiple studies, including a major analysis by the Academy of Nutrition and Dietetics, have shown it to be the most reliable for most adults.

Male: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5

Female: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161

Best for: most adults, especially those of average or mixed body composition.

Harris-Benedict (Revised) Classic — Slightly Higher

The original Harris-Benedict equation (1919) was revised by Roza and Shizgal in 1984. It was the gold standard for decades and is still widely used in clinical settings. It tends to overestimate BMR by 5–15% compared to Mifflin-St Jeor, particularly for overweight individuals.

Male: BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)

Female: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)

Best for: clinical settings, historical reference, comparison with older estimates.

Katch-McArdle Most Precise if BF% Known

The Katch-McArdle formula is unique in that it uses lean body mass (LBM) rather than total body weight. Because body fat is metabolically less active than lean tissue, LBM-based formulas are more accurate for athletes, muscular individuals, and anyone who knows their body fat percentage.

BMR = 370 + (21.6 × Lean Body Mass in kg)

Lean Body Mass = Weight × (1 − Body Fat% ÷ 100)

Best for: athletes, gym-goers, anyone who knows their body fat %. Requires body fat % input.

Which Formula Should You Use?

Don't know body fat %? → Use Mifflin-St Jeor (Auto default)
Know body fat %? → Use Katch-McArdle for best accuracy
Athletic build? → Katch-McArdle is especially valuable — it won't underestimate your BMR due to high muscle mass
Comparing with old estimates? → Harris-Benedict may match historical numbers better
Unsure? → Leave it on Auto and trust the formula comparison in results

BMR vs TDEE vs RMR — Key Differences

Term	Full Name	What It Measures	Includes Activity?	Use Case
BMR	Basal Metabolic Rate	Calories at complete rest (fasted, lying still)	No	Foundation for all calorie calculations
RMR	Resting Metabolic Rate	Calories at rest (less strict conditions)	No (minimal)	Clinical measurement; ≈ BMR in practice
TDEE	Total Daily Energy Expenditure	All calories burned daily including exercise	Yes	Set weight loss/maintenance/gain targets
TEF	Thermic Effect of Food	Calories burned digesting food (~10% of intake)	Partial	Included in TDEE estimate; higher for protein
NEAT	Non-Exercise Activity Thermogenesis	Calories from non-exercise movement (fidgeting, walking)	Yes	Highly variable; largest wild card in TDEE

What Factors Affect Your BMR?

Factors That Increase BMR

More lean muscle mass: Muscle burns ~13 kcal/kg/day at rest vs ~4 kcal/kg/day for fat. Resistance training is the most effective long-term BMR booster.
Being male: Men typically have more muscle mass and lower body fat, resulting in higher average BMR for the same height and weight.
Taller stature: More surface area means more organ mass and higher resting energy demands.
Younger age: BMR peaks in your 20s and declines by ~1–2% per decade, primarily due to muscle loss.
Hyperthyroidism: Excess thyroid hormones dramatically increase metabolic rate.
Fever: Each 1°C increase in body temperature raises BMR by ~7–13%.
Pregnancy: Growing a baby significantly increases metabolic demands.

Factors That Decrease BMR

Muscle loss (sarcopenia): The primary driver of age-related BMR decline. Sedentary lifestyles accelerate this.
Caloric restriction: Severely restricting calories causes adaptive thermogenesis — your body lowers BMR to conserve energy.
Hypothyroidism: Underactive thyroid significantly reduces metabolic rate.
Older age: BMR decreases steadily after age 25–30 due to hormonal changes and muscle loss.
Fasting: Extended fasting triggers metabolic adaptation, reducing BMR by 10–20%.
Low-calorie dieting: Chronic dieting can suppress BMR, making further weight loss progressively harder.
Cold adaptation: Paradoxically, long-term cold exposure can reduce BMR through brown fat adaptation.

Average BMR Reference Table by Age & Sex

These averages are based on typical height/weight ranges using the Mifflin-St Jeor formula. Individual BMR varies significantly based on body composition.

Age Group	Average Male BMR	Average Female BMR	Typical Height (M/F)	Typical Weight (M/F)
18–24	~1,850 kcal	~1,480 kcal	178 / 164 cm	75 / 62 kg
25–34	~1,820 kcal	~1,455 kcal	178 / 164 cm	78 / 65 kg
35–44	~1,780 kcal	~1,420 kcal	178 / 164 cm	82 / 68 kg
45–54	~1,730 kcal	~1,375 kcal	177 / 163 cm	84 / 70 kg
55–64	~1,680 kcal	~1,330 kcal	176 / 162 cm	85 / 72 kg
65–74	~1,615 kcal	~1,280 kcal	175 / 161 cm	82 / 70 kg
75+	~1,545 kcal	~1,230 kcal	173 / 159 cm	78 / 66 kg

These are population estimates only. Athletes, those with high muscle mass, and very tall or heavy individuals will have significantly higher BMRs.

Frequently Asked Questions — BMR Calculator

BMR (Basal Metabolic Rate) is the number of calories your body needs to sustain basic functions at complete rest — breathing, heartbeat, organ function, and cell repair. It matters because it forms the foundation of every calorie target. If your goal is weight loss, maintenance, or muscle gain, you need to know your BMR first to set an accurate TDEE and calorie goal.

BMR is your calorie burn at complete rest. TDEE (Total Daily Energy Expenditure) adds all physical activity on top of BMR. TDEE = BMR × Activity Multiplier. For weight management, you set your calorie intake relative to TDEE — not BMR. Eating at TDEE maintains weight; eating below TDEE creates a deficit for fat loss; eating above TDEE creates a surplus for muscle gain.

For most people, Mifflin-St Jeor is the most accurate and is the current recommendation of the Academy of Nutrition and Dietetics. If you know your body fat percentage, Katch-McArdle is more precise because it uses lean body mass directly — this is especially valuable for athletes or muscular individuals where BMR would be underestimated by weight-based formulas. Harris-Benedict tends to overestimate by 5–15% and is considered slightly outdated.

No. You should eat below your TDEE (not BMR) to lose weight. BMR is the minimum calories for basic organ function. Consistently eating at or below BMR signals a starvation response, causing your body to slow metabolism (adaptive thermogenesis), break down muscle for energy, and conserve fat. A healthy deficit is 10–25% below your TDEE, which corresponds to 0.25–0.75 kg of fat loss per week.

Yes. BMR typically declines by approximately 1–2% per decade after age 20. The primary cause is loss of lean muscle mass (sarcopenia), not age itself. This is why two people of the same age can have dramatically different BMRs — the one with more muscle has a significantly higher resting calorie burn. Regular resistance training throughout life is the most evidence-based strategy to slow this decline.

The most effective way to increase BMR is to build and preserve lean muscle mass through progressive resistance training. Other strategies include: eating adequate protein (0.8–1.2g per kg of body weight minimally) to prevent muscle loss; avoiding severe caloric restriction which suppresses BMR; optimizing thyroid health through micronutrient sufficiency (iodine, selenium, zinc); and maintaining a healthy body weight (both obesity and underweight are associated with metabolic dysfunction).

Adaptive thermogenesis (also called metabolic adaptation) is the process by which your body reduces its energy expenditure in response to sustained caloric restriction. When you diet, your body not only lowers BMR but also reduces NEAT (unconscious movement) and increases appetite hormones. This is why weight loss typically plateaus after several weeks. To counteract it: incorporate diet breaks, reverse diet periods, prioritize resistance training, and eat adequate protein.

Activity multipliers are: Sedentary (desk job, no exercise): 1.2 | Lightly Active (1–3 exercise sessions/week): 1.375 | Moderately Active (3–5 sessions/week): 1.55 | Very Active (6–7 hard sessions/week): 1.725 | Extra Active (physical labor + daily exercise): 1.9. When in doubt, most people tend to overestimate activity — start with Lightly Active or Moderately Active and adjust based on real-world results after 2–3 weeks.