Free BMR & TDEE Calculator

Calculate your basal metabolic rate using 3 formulas and find your total daily energy expenditure — with an activity table, weight-goal scenarios, and macro breakdown.

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3 BMR Formulas Compared
Mifflin-St Jeor (1990) — Recommended
Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
Most accurate for the general population. Predicts measured BMR within ±10% for ~80% of people.
Harris-Benedict (Revised 1984)
Men: (13.397 × kg) + (4.799 × cm) − (5.677 × age) + 88.362
Women: (9.247 × kg) + (3.098 × cm) − (4.330 × age) + 447.593
Classic formula, slightly overestimates for sedentary individuals. Widely used in clinical settings.
Katch-McArdle — Best for Athletes
BMR = 370 + (21.6 × Lean Body Mass kg)
LBM = weight × (1 − body fat% ÷ 100)
Uses lean mass, not total weight — most accurate for athletic or muscular individuals who know their body fat %.

Which BMR Formula Should You Use?

All three formulas estimate BMR from easily measurable inputs. They differ in what variables they use and the populations they were validated against.

Mifflin-St Jeor (1990) is the current gold standard for the general population. It was derived from a modern, representative sample and validated against measured metabolic data. The Academy of Nutrition and Dietetics recommends it for clinical use.

Harris-Benedict (originally 1919, revised 1984) is the historic standard. The revised version performs comparably to Mifflin-St Jeor for most people but tends to overestimate BMR slightly for sedentary individuals.

Katch-McArdle is the most accurate formula if you know your body fat percentage. Because it uses lean body mass instead of total weight, it correctly handles the fact that muscle tissue burns significantly more calories than fat at rest.

Not sure which to pick? Use Mifflin-St Jeor for everyday planning. Use Katch-McArdle if you're athletic, have a DEXA scan or body pod measurement of your body fat %, and want the most accurate result.

If you're applying these formulas specifically to fat loss, our step-by-step guide on how to calculate BMR for weight loss walks through all three formulas with worked examples, common mistakes, and a full action plan.

Activity Level Guide
×1.2
Sedentary
Desk job, no structured exercise. Typical office worker.
×1.375
Lightly Active
30–45 min of light exercise (walk, yoga) 1–3×/week.
×1.55
Moderately Active ← Most people
Gym or cardio 3–5×/week for 30–60 min.
×1.725
Very Active
Hard training 6–7×/week or intense sport.
×1.9
Extra Active
Twice-daily training, athlete, or labour-intensive job.
Common mistake: Most people choose "Very Active" when they're actually "Moderately Active." Overestimating activity level is the #1 reason calorie tracking fails.

Understanding TDEE & Activity Multipliers

Your TDEE is your BMR multiplied by an activity factor that accounts for all the ways you burn calories beyond basic bodily functions — structured exercise, incidental movement (NEAT), and digestion.

The five standard multipliers were established in research on military personnel and later validated broadly. They are estimates — individual TDEE can vary ±15% from formula predictions due to genetics, body composition, and movement efficiency.

  • NEAT (Non-Exercise Activity Thermogenesis) — calories burned by all movement that isn't formal exercise: walking between meetings, fidgeting, standing, cleaning. NEAT can vary by up to 2,000 kcal/day between individuals, making it the largest driver of TDEE variation.
  • TEF (Thermic Effect of Food) — digestion costs roughly 10% of calories consumed. Protein has the highest TEF (~25–30%), meaning a high-protein diet slightly increases TDEE.
  • Metabolic adaptation — chronic calorie restriction causes TDEE to fall 5–15% below what the formula predicts, as the body adjusts hormone levels and reduces NEAT.
Track don't guess. The most accurate way to know your TDEE is to eat a consistent number of calories for 3–4 weeks and observe weight change. If weight is stable, that intake = your TDEE.

What Affects Your BMR? 7 Key Factors

Your BMR is not fixed — these factors shift it significantly over time.

Muscle Mass
Muscle tissue burns ~6 kcal/kg/day at rest versus ~2 kcal/kg/day for fat. Every kilogram of muscle added raises BMR by roughly 13 kcal/day. Strength training is the most effective way to permanently increase BMR.
Age
BMR declines approximately 2% per decade after age 20, primarily because muscle mass decreases (sarcopenia). By age 60, BMR can be 15–20% lower than at age 20. Regular resistance training significantly slows this decline.
Thyroid Function
The thyroid gland is the primary regulator of metabolic rate. Hypothyroidism can reduce BMR by 30–40%; hyperthyroidism can raise it by 50–100%. Unexplained weight gain or difficulty losing weight warrants a thyroid panel.
Biological Sex
Men have a higher BMR than women of the same age, height, and weight — primarily because men carry more lean mass on average. The difference is typically 5–10% and is already accounted for in all three calculator formulas.

Frequently Asked Questions About BMR & TDEE

Science-backed answers to the most common questions.

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — the minimum energy needed to keep you alive. It accounts for 60–70% of your total daily calorie burn. Knowing your BMR gives you a floor: eating below your BMR for extended periods can trigger metabolic adaptation and muscle breakdown.
For most people: Mifflin-St Jeor (1990). Research shows it predicts measured BMR within ±10% for ~80% of the population and outperforms the older Harris-Benedict equation. For lean, athletic individuals who know their body fat percentage: Katch-McArdle is more accurate because it uses lean body mass rather than total weight.
TDEE = BMR × Activity Multiplier. The five standard multipliers are: Sedentary (×1.2), Lightly Active (×1.375), Moderately Active (×1.55), Very Active (×1.725), Extra Active (×1.9). The TDEE tab shows your result for all five activity levels simultaneously so you can see the full range.
Eat 250–500 kcal below your TDEE for safe fat loss. A 500 kcal/day deficit produces approximately 0.5 kg (1 lb) of fat loss per week. Deficits above 1,000 kcal/day are not recommended — they risk muscle loss, metabolic adaptation, and nutritional deficiencies. Minimum safe intake is ~1,200 kcal/day for women, ~1,500 kcal/day for men.
Katch-McArdle calculates BMR from lean body mass: BMR = 370 + (21.6 × LBM kg), where LBM = weight × (1 − body fat% ÷ 100). Use it if you know your body fat % from a reliable source (DEXA, hydrostatic weighing, body pod) and are athletic or lean. It's not suitable if your body fat % is estimated from photos or inaccurate methods.
Different calculators use different formulas (Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle), which produce results that differ by 2–10%. Our calculator shows all three side by side so you can see the full range. Also check that you're entering the same units (kg/cm vs lbs/ft) — a common source of discrepancy.
Yes — this is called metabolic adaptation. When you eat in a sustained calorie deficit, your body reduces BMR by 5–15% through hormonal changes (lower leptin, lower T3 thyroid hormone) and reduced NEAT. This is why fat loss slows over time even without changing intake. Diet breaks and refeeds help partially restore metabolic rate.
BMR requires strict measurement conditions: 12-hour fast, fully rested, lying still, temperature-controlled environment. RMR (Resting Metabolic Rate) is measured at rest without strict fasting. RMR is typically 10–20% higher than BMR. Online calculators technically estimate RMR — but the terms are used interchangeably in everyday practice.

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