What is BMR and why does it matter?

BMR is the calories your body burns at complete rest. It sets the minimum calorie floor — eating below it long-term causes muscle loss and metabolic adaptation.

Which BMR formula is most accurate?

Mifflin–St Jeor is most accurate for most adults. Katch–McArdle is better for athletes who know their body-fat percentage.

What is TDEE and how is it different from BMR?

BMR is calories at rest. TDEE is total daily calories including all activity. TDEE = BMR × activity multiplier.

How many calories should I eat to lose weight?

Subtract 500 kcal/day from your TDEE for approximately 0.45 kg (1 lb) of fat loss per week. Don't eat below your BMR without medical supervision.

Does BMR change if I lose weight?

Yes. BMR decreases as body weight decreases. Recalculate every 4–6 weeks during a diet to keep targets accurate.

Fitness & Health

Find your BMR & daily calorie needs

Enter your age, gender, height, weight, and activity level. Get your Basal Metabolic Rate, TDEE across all five activity levels, and calorie targets for weight loss, maintenance, and gain.

3 BMR formulas Metric & imperial 5 activity levels TDEE table Weight-goal calories Katch–McArdle support

BMR Calculator

Basal Metabolic Rate & TDEE

Gender

Units

Age

yrs

Weight (kg)

Height (cm)

BMR Formula

Your BMR

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calories at complete rest per day

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Daily Calorie Needs by Activity Level

Activity Level	Multiplier	Calories/day
Sedentary (little/no exercise)	× 1.2	—
Lightly active (1–3 days/week)	× 1.375	—
Moderately active (3–5 days/week)	× 1.55	—
Very active (6–7 days/week)	× 1.725	—
Extra active (physical job + exercise)	× 1.9	—

Calorie Targets (Moderately Active)

Lose ~0.45 kg/week TDEE − 500 kcal

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Maintain weight At TDEE

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Lean bulk ~0.45 kg/week TDEE + 500 kcal

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These are estimates (±10%). Recalculate every 4–6 weeks as your weight changes.

BMR & TDEE Calculator — How Many Calories Do You Actually Need?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns every day just to keep you alive — breathing, circulating blood, maintaining body temperature, and powering your organs while completely at rest. It accounts for 60–75% of total daily calorie expenditure for most people.

Your Total Daily Energy Expenditure (TDEE) builds on your BMR by factoring in how physically active you are. If you want to lose, maintain, or gain weight, TDEE is the number you work from — eating below it causes weight loss, above it causes gain.

This calculator supports three clinically validated BMR formulas and automatically generates a full TDEE table for all five activity levels, plus daily calorie targets for common weight goals.

The Three BMR Formulas Explained

Recommended

Mifflin–St Jeor (1990)

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

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

The most accurate formula for the general adult population. Validated by the American Dietetic Association as the preferred equation for estimating calorie needs in most clinical and non-clinical settings.

Revised Harris–Benedict (1984)

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

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

The classic formula revised by Roza & Shizgal for improved accuracy. Slightly overestimates BMR compared to Mifflin–St Jeor but remains widely used and clinically accepted.

Katch–McArdle (1975)

BMR: 370 + (21.6 × Lean Mass kg)

Lean mass: weight × (1 − body fat %)

Uses lean body mass instead of total weight — ignores fat entirely. Ideal for athletes and muscular individuals whose body composition differs from population averages. Requires knowing your body-fat percentage.

TDEE Activity Level Multipliers

TDEE is calculated by multiplying your BMR by an activity factor that reflects how much you move each day:

Activity Level	Description	Multiplier
Sedentary	Desk job, little or no exercise	× 1.2
Lightly active	Light exercise 1–3 days/week	× 1.375
Moderately active	Moderate exercise 3–5 days/week	× 1.55
Very active	Hard exercise 6–7 days/week	× 1.725
Extra active	Very hard exercise + physical job	× 1.9

These are the Harris–Benedict activity factors used across virtually all TDEE calculators. They're averages — real-world TDEE can vary ±10–20% based on non-exercise activity thermogenesis (NEAT), sleep, and individual metabolism.

Using Your BMR & TDEE for Weight Goals

Weight Loss Create a calorie deficit below your TDEE. A deficit of 500 kcal/day produces roughly 0.45 kg (1 lb) of fat loss per week. A 1,000 kcal deficit targets ~0.9 kg/week — generally the safe maximum. Never eat below your BMR without medical supervision.

Weight Maintenance Eat at TDEE. This is the number of calories that keeps your current weight stable. Small fluctuations day-to-day are normal — what matters is the weekly average staying near TDEE.

Muscle Gain (Lean Bulk) Eat 250–500 kcal above TDEE. A modest surplus allows muscle growth with minimal fat gain. Pair with progressive resistance training for best results. Aggressive bulking (1,000+ kcal surplus) adds significant fat alongside muscle.

Practical tip: Your TDEE is an estimate, not a precise measurement. Track your actual weight trend over 2–3 weeks while eating at your calculated TDEE — if you're gaining or losing weight, adjust calories by 100–200 kcal and re-evaluate.

Why BMR Changes Over Time

BMR is not fixed — several factors cause it to shift throughout your life:

Age BMR declines approximately 1–2% per decade after age 20, primarily due to the natural loss of muscle mass (sarcopenia). Strength training slows this decline.

Muscle Mass Muscle is metabolically expensive — it burns ~6× more calories at rest than fat tissue. More muscle = higher BMR. This is why the Katch–McArdle formula can be more accurate for athletes.

Dieting Prolonged caloric restriction causes adaptive thermogenesis — the body reduces BMR to conserve energy. This is "metabolic adaptation" and explains why weight loss plateaus after sustained restriction.

Hormones Thyroid hormones directly regulate metabolic rate. Hypothyroidism lowers BMR; hyperthyroidism raises it. Cortisol, insulin, testosterone, and estrogen also influence metabolism.

How to Use This BMR Calculator

Select your gender — the BMR formulas differ by sex due to differences in average body composition.
Choose metric or imperial — metric uses kg and cm; imperial uses lb, ft, and inches.
Enter your age — required by all three formulas as BMR decreases with age.
Enter weight and height — use your current weight and accurate height measurement.
Choose a formula — Mifflin–St Jeor for most people; Katch–McArdle if you know your body-fat %.
Enter body-fat % (if using Katch–McArdle) — your approximate body-fat percentage from any reliable measurement.
Click "Calculate BMR" — your BMR and full TDEE table appear with weight-goal calorie rows.

Frequently Asked Questions

Basal Metabolic Rate is the calories your body burns at complete rest — no movement, no digestion — just basic life support. It matters because it sets the floor for how many calories you need. Eating below your BMR long-term can cause muscle loss, hormonal disruption, and metabolic adaptation.

For most non-athletic adults, Mifflin–St Jeor is the most accurate — validated studies show it comes closest to measured BMR. For athletes or muscular individuals, Katch–McArdle is more accurate because it uses lean body mass and ignores fat, which burns very few calories at rest. Harris–Benedict slightly overestimates for many modern adults.

BMR is calories burned at rest. TDEE is total calories burned in a day including all physical activity. TDEE = BMR × activity multiplier. For a sedentary person, TDEE is about 20% above BMR. For a very active person, TDEE can be 70–90% above BMR. TDEE is the number you use for setting calorie targets.

Subtract 500 kcal from your TDEE for your activity level to target approximately 0.45 kg (1 lb) of fat loss per week. Subtract 1,000 kcal for ~0.9 kg/week — the generally accepted safe maximum. Going below your BMR is not recommended without medical supervision, as it risks muscle loss and metabolic adaptation.

Use the Mifflin–St Jeor formula instead. For body-fat estimation, you can use a body fat calculator (which uses circumference measurements), DEXA scan, underwater weighing, or bioelectrical impedance scales. Even a rough estimate (e.g. 18% for an average adult male) will give a more accurate Katch–McArdle result than using no formula at all.

Each formula was derived from a different study population using different measurement methods. Mifflin–St Jeor used indirect calorimetry (the gold standard) on 498 people in 1990. Harris–Benedict dates to 1919 and was revised in 1984. Katch–McArdle focuses on lean mass. No formula is "correct" — they're all estimates with roughly ±10% accuracy for individuals.

Yes. BMR decreases as you lose weight because smaller bodies require fewer calories at rest. Additionally, prolonged caloric restriction causes "adaptive thermogenesis" — the body further reduces BMR beyond what the weight loss alone predicts. This is why recalculating BMR every 4–6 weeks during a diet is important for accurate targets.

These formulas are validated for adults (18+). Children and teenagers have different metabolic profiles and growth energy requirements. For under-18s, paediatric BMR equations or a healthcare provider should be consulted.

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How to Use This BMR Calculator

Frequently Asked Questions

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