BMR Calculator | Basal Metabolic Rate & TDEE
Calculate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) using Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas. Compare all three formulas and see daily calorie targets by goal.
Quick examples
BMR formula
What Is the BMR Calculator | Basal Metabolic Rate & TDEE?
Basal Metabolic Rate (BMR) is the minimum number of calories your body requires to sustain vital functions, heartbeat, breathing, thermoregulation, brain activity, and cell repair, while at complete rest and in a fasted state. It represents roughly 60–70% of your total daily calorie expenditure.
Total Daily Energy Expenditure (TDEE) multiplies BMR by an activity factor to estimate how many calories you actually burn in a typical day including exercise, non-exercise activity (fidgeting, walking, housework), and the thermic effect of food. TDEE is your true maintenance calorie level.
The Mifflin-St Jeor equation, used by default, was validated in a 1990 study across men and women of varying body sizes and outperformed older formulas by being accurate within ±10% for approximately 82% of participants. It is the formula recommended by the Academy of Nutrition and Dietetics (AND) for most clinical applications.
The Katch-McArdle formula bypasses the sex correction entirely and works directly from lean body mass (LBM). Because muscle tissue drives most of resting metabolism, knowing your actual LBM (via DEXA, hydrostatic weighing, or the Navy method) makes Katch-McArdle the most precise option for athletes and anyone with above-average muscle mass.
Formula
Mifflin-St Jeor (1990), recommended
Female: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Harris-Benedict Revised (Roza & Shizgal, 1984)
Female: BMR = 447.593 + 9.247w + 3.098h − 4.330a
(w = kg, h = cm, a = years)
Katch-McArdle, uses lean body mass
BMR = 370 + 21.6 × LBM
Sex-agnostic, only lean mass matters. Requires an accurate body fat % measurement.
TDEE formula
| Activity Level | Description | Multiplier | Typical users |
|---|---|---|---|
| Sedentary | Desk work, little or no deliberate exercise | ×1.2 | office workers, remote workers |
| Lightly Active | Light exercise 1–3 days per week | ×1.375 | walkers, occasional gym-goers |
| Moderately Active | Moderate exercise 3–5 days per week | ×1.55 | most recreational athletes |
| Very Active | Hard training 6–7 days per week | ×1.725 | endurance athletes in training |
| Extra Active | Physical labour job or twice-daily training | ×1.9 | construction workers, elite athletes |
| Formula | Equation | Accuracy / notes |
|---|---|---|
| Mifflin-St Jeor (1990) | 10w + 6.25h − 5a + 5 (M) / −161 (F) | Best overall accuracy; ±10% for most adults |
| Harris-Benedict Revised (1984) | 88.362 + 13.397w + 4.799h − 5.677a (M) | Slightly overestimates; widely used in clinical settings |
| Katch-McArdle (1975/2002) | 370 + 21.6 × LBM | Most accurate when body fat % is known; sex-agnostic |
How to Use
- 1Choose units: Select Metric (kg, cm) or Imperial (lb, ft & in). All values auto-convert on switch.
- 2Select sex: Choose Male or Female, the sex adjustment accounts for differences in average lean mass and hormonal baseline metabolism.
- 3Choose a formula: Mifflin-St Jeor is the default and works for most people. Choose Harris-Benedict for clinical comparison, or Katch-McArdle if you know your body fat percentage.
- 4Enter your stats: Fill in age, weight, height, and optionally body fat %. All inputs are auto-saved so you can return to them later.
- 5Set activity level: Pick the activity multiplier that best reflects a typical week, most people overestimate, so choose conservatively.
- 6Calculate: Click "Calculate BMR & TDEE" (or press Enter). See your BMR, TDEE, a full activity comparison table, goal-based calorie targets, and a side-by-side formula comparison.
- 7Reset if needed: Click Reset All or press Esc to clear everything and start fresh. Use the preset buttons to instantly load common profiles.
Example Calculation
Example 1, 30-year-old woman, metric, Mifflin-St Jeor
BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161
= 650 + 1031.25 − 150 − 161
= 1,370 kcal/day
Activity: Moderately Active (×1.55)
TDEE = 1,370 × 1.55 = 2,124 kcal/day
Weight loss target: 2,124 − 500 = 1,624 kcal/day (≈ −0.5 kg/week)
Example 2, 35-year-old man, imperial, Katch-McArdle
LBM = 83.9 × (1 − 0.15) = 83.9 × 0.85 = 71.3 kg
BMR = 370 + 21.6 × 71.3 = 370 + 1,540 = 1,910 kcal/day
Mifflin-St Jeor for same person:
BMR = 10 × 83.9 + 6.25 × 182.9 − 5 × 35 + 5 = 1,888 kcal/day
Activity: Very Active (×1.725)
TDEE (Katch) = 1,910 × 1.725 = 3,295 kcal/day
Example 3, Formula comparison, 45-year-old sedentary man, 90 kg, 180 cm
Harris-Benedict: 88.36 + 13.40×90 + 4.80×180 − 5.68×45 = 1,970 kcal
Difference: Harris overpredicts by ~90 kcal/day (≈ 5%)
TDEE (Sedentary ×1.2):
Mifflin → 2,256 kcal | Harris → 2,364 kcal
Understanding BMR | Basal Metabolic Rate & TDEE
What is Basal Metabolic Rate and why does it matter?
Your body never truly switches off. Even while you sleep, it burns energy to maintain your core temperature, contract your heart muscle roughly 100,000 times a day, repair cellular damage, synthesise hormones, and perform hundreds of other involuntary functions. BMR quantifies the calorie cost of all of this activity at the theoretical minimum, complete rest, after an overnight fast, in a thermoneutral environment.
In practical nutrition planning, BMR is the floor. You will always burn at least this many calories just by being alive, and any sustained intake below BMR is medically inadvisable without clinical supervision. Understanding your BMR gives you the lower boundary of any calorie target, a safeguard against overly aggressive deficits.
More importantly, BMR multiplied by your activity factor gives TDEE, the number that actually drives weight change. Eat at TDEE and weight stays stable. Eat below and you lose; above and you gain. Precise knowledge of TDEE is the foundation of any evidence-based nutrition plan.
The Mifflin-St Jeor equation, why it's the gold standard
Published in 1990 by Mark Mifflin and Sachiko St Jeor, this equation was developed from a carefully controlled study of 498 healthy adults (men and women) spanning a broad range of ages and body compositions. The researchers used indirect calorimetry, the most accurate non-invasive method for measuring metabolic rate, as the gold standard against which all formula predictions were validated.
The result: Mifflin-St Jeor predicted resting energy expenditure within 10% for 82% of subjects, outperforming both the original and revised Harris-Benedict equations. The Academy of Nutrition and Dietetics reviewed the evidence in 2005 and recommended Mifflin-St Jeor as the preferred predictive equation for most adults.
- ›Works well for normal-weight, overweight, and moderately obese adults
- ›Simple inputs: weight (kg), height (cm), age (years), sex
- ›Sex difference captured by the +5 (male) / −161 (female) constant
- ›Consistent ±10% accuracy across diverse populations
Harris-Benedict vs Mifflin-St Jeor, history and accuracy
The Harris-Benedict equation predates Mifflin-St Jeor by more than 70 years. The original 1919 formula by James Harris and Francis Benedict was based on just 239 subjects, a small, predominantly white, physically active sample that does not reflect modern sedentary populations. It was revised in 1984 by Roza and Shizgal using updated data, which is the version this calculator uses.
Even the revised Harris-Benedict consistently overestimates BMR by approximately 5% for the average sedentary adult, around 90–120 kcal/day. That might seem small, but over a week it adds up to a 630–840 kcal discrepancy, which can stall weight loss or cause inadvertent fat gain if TDEE is systematically inflated.
When is Harris-Benedict still useful?
Some clinical dietitians still use Harris-Benedict for established institutional protocols, or when comparing a patient's historical records. For general use, always prefer Mifflin-St Jeor. This calculator shows both side by side so you can see the difference.
Katch-McArdle: the lean mass approach for athletes
The Katch-McArdle formula discards weight and height entirely and works only from lean body mass (LBM), the portion of your weight that is not body fat. The logic is physiologically sound: fat tissue is metabolically inert relative to muscle. Two people with the same weight but different body compositions will have significantly different BMR values, and only Katch-McArdle captures this.
- ›Formula: BMR = 370 + 21.6 × LBM(kg)
- ›LBM = total weight × (1 − body fat fraction)
- ›Sex-agnostic, a 70 kg man and a 70 kg woman with identical LBM get identical BMR predictions
- ›Most accurate for athletes, bodybuilders, and anyone with above-average muscle mass
- ›Body fat % must be measured accurately, the formula is only as good as this input
Use our Body Fat Calculator (US Navy method) to estimate your body fat percentage if you don't have a DEXA or hydrostatic weighing result. Enter the result here to unlock the Katch-McArdle formula.
Understanding TDEE activity multipliers
The activity multipliers, from ×1.2 for sedentary to ×1.9 for extra active, were originally derived from population-level doubly labelled water studies, which measure true energy expenditure over real-world conditions. They are intentionally broad buckets; individual variation within each category can be significant.
The most common mistake is overestimating activity level. Most adults who “exercise three times per week” are Lightly Active (×1.375) rather than Moderately Active (×1.55), because the remainder of their day is sedentary. Choosing the next category up inflates TDEE by roughly 175–225 kcal/day, a meaningful error.
- ›If your job is desk-based and you exercise 3–5 days/week, choose Lightly Active or Moderately Active, not Very Active
- ›If you train daily for sport, add recovery days and rest the formula correctly: choose Very Active
- ›Physical labourers (construction, warehousing, farming) who also train may qualify for Extra Active
- ›When in doubt, choose a lower multiplier and adjust upward if weight trends incorrectly over 2–3 weeks
How to use your BMR and TDEE for weight management
Once you know your TDEE, weight management becomes a straightforward arithmetic exercise:
- ›Fat loss: Create a 500 kcal/day deficit (TDEE − 500). This yields approximately 0.5 kg/week of fat loss, the rate most supported by evidence for preserving lean mass
- ›Aggressive fat loss: A 750 kcal/day deficit (TDEE − 750) targets 0.75 kg/week. Do not go lower without medical supervision, muscle loss accelerates below BMR
- ›Lean muscle gain: A modest surplus of 200–300 kcal/day above TDEE minimises fat gain during a building phase. Combine with progressive resistance training
- ›Weight maintenance: Eat at TDEE. Adjust every 4–6 weeks as your weight changes, BMR drops slightly with weight loss, so TDEE decreases too
Use our Calorie Calculator for a more detailed TDEE breakdown, and our Macro Calculator to translate your calorie target into protein, carbohydrate, and fat grams.
Factors that influence your actual BMR
All BMR formulas are statistical estimates. Your true resting metabolic rate depends on several factors that no equation fully captures:
- ›Lean muscle mass, each kg of muscle burns ~13 kcal/day at rest vs ~4.5 kcal/day for fat tissue. Resistance training raises BMR by increasing LBM over time
- ›Age, BMR declines roughly 1–2% per decade after age 30, primarily due to sarcopenia (muscle loss) rather than ageing per se
- ›Thyroid hormones, hypothyroidism can reduce BMR by 30–40%; hyperthyroidism can increase it by 25–80%
- ›Genetic variation, twin studies estimate that ~40–70% of inter-individual BMR variation is heritable
- ›Calorie restriction history, prolonged dieting can suppress BMR via adaptive thermogenesis, independent of lean mass loss
- ›Pregnancy and lactation, significantly increases metabolic needs; consult a healthcare provider for adjusted targets
For related health metrics, also try our BMI Calculator and Ideal Weight Calculator to build a complete picture of your health baseline.
Frequently Asked Questions
What is the difference between BMR and TDEE?
They measure different things and serve different purposes:
- ›BMR (Basal Metabolic Rate): calories your body burns at complete rest, just to stay alive with no movement at all
- ›TDEE (Total Daily Energy Expenditure): calories you burn in a real day, including exercise, walking, daily tasks, and the thermic effect of food
- ›TDEE = BMR × activity multiplier (typically ×1.2 to ×1.9)
- ›BMR is the floor; TDEE is the target for nutrition planning
Use BMR as a safety minimum (never eat below it long-term) and TDEE as your maintenance baseline.
Which BMR formula is most accurate?
It depends on your situation:
- ›Mifflin-St Jeor (1990): most accurate for the general population, recommended by the Academy of Nutrition and Dietetics. Best default choice.
- ›Katch-McArdle: most accurate for athletes and muscular individuals when you know your body fat %. Bypasses the sex variable and uses lean mass directly.
- ›Harris-Benedict Revised (1984): historically important but consistently overestimates BMR by ~5% vs Mifflin-St Jeor. Still used in some clinical protocols.
For most people: use Mifflin-St Jeor. For athletes with known body fat percentage: use Katch-McArdle.
Why does Katch-McArdle need body fat percentage?
The Katch-McArdle formula works from lean body mass (LBM) rather than total weight, because lean mass, not fat, drives resting metabolism:
- ›Muscle tissue burns ~13 kcal/kg/day at rest
- ›Fat tissue burns only ~4.5 kcal/kg/day at rest
- ›Two people weighing 80 kg with 10% vs 30% body fat will have very different BMRs
- ›Body fat % lets the formula isolate the metabolically active portion of your body
LBM = total weight × (1 − body fat fraction). Enter your body fat % from DEXA, hydrostatic weighing, or our Body Fat Calculator (US Navy method) for the most accurate result.
What activity level should I choose?
Most people overestimate their activity level. Use these guidelines:
- ›Sedentary (×1.2): desk job, sitting most of the day, little to no deliberate exercise
- ›Lightly Active (×1.375): exercise 1–3 days/week but sedentary at work, this covers most casual gym-goers
- ›Moderately Active (×1.55): structured exercise 3–5 days/week with moderate intensity
- ›Very Active (×1.725): hard daily training or physically demanding job plus regular exercise
- ›Extra Active (×1.9): twice-daily training sessions OR physically demanding labour job with additional exercise
When unsure, choose the lower option and track your weight for 2–3 weeks. Adjust upward if weight drops faster than expected.
Is eating below my BMR dangerous?
Consistently eating well below your BMR (rather than your TDEE) carries real risks:
- ›Accelerated lean muscle loss, your body catabolises muscle for energy when calories are severely restricted
- ›Adaptive thermogenesis, the body down-regulates non-essential metabolic processes, lowering actual BMR below the calculated value
- ›Nutritional deficiencies, very-low-calorie diets are hard to make nutritionally complete
- ›Hormonal disruption, especially sex hormones, thyroid function, and cortisol
- ›Metabolic adaptation, prolonged sub-BMR eating makes subsequent weight loss progressively harder
Short-term medical very-low-calorie diets (400–800 kcal) exist and can be effective under clinical supervision. Without supervision, maintain at least 1,200 kcal/day for women and 1,500 kcal/day for men as a general lower bound.
How often should I recalculate my BMR?
BMR changes whenever your body composition or age changes significantly:
- ›After every 5 kg (11 lb) of weight change, BMR shifts enough to affect your TDEE meaningfully
- ›Every 3–6 months during an active cut or bulk, weight changes regularly during these phases
- ›When changing activity level, a new job, starting a sport, or stopping training changes your multiplier
- ›After a prolonged diet break, adaptive thermogenesis may have reduced your actual BMR
- ›At each birthday decade (30s, 40s, 50s) as age-related metabolic slowdown becomes meaningful
This calculator saves your last inputs automatically, so recalculating with updated numbers only takes seconds.
Does building muscle increase my BMR?
Yes, and this is one of the most powerful long-term metabolic strategies available:
- ›Each additional kg of lean muscle increases resting calorie burn by approximately 13 kcal/day
- ›Gaining 5 kg of lean mass raises BMR by roughly 65 kcal/day, an extra ~450 kcal/week burned at rest
- ›Resistance training itself also elevates metabolism for 24–48 hours post-session via excess post-exercise oxygen consumption (EPOC)
- ›Higher LBM means the Katch-McArdle formula gives you a higher (and more accurate) BMR estimate
This is why strength training is consistently recommended alongside calorie restriction for weight management, it protects lean mass and prevents the BMR decline associated with pure calorie-deficit dieting.
Why is my calculated BMR different from what my fitness tracker shows?
Several factors explain the discrepancy:
- ›Different formulas, Fitbit, Apple Watch, and Garmin each use proprietary algorithms that may differ from Mifflin-St Jeor
- ›Activity adjustment, wearables apply real-time movement data; this calculator uses fixed activity multipliers
- ›Heart rate data, some wearables adjust calorie estimates based on heart rate, which can improve or worsen accuracy depending on sensor quality
- ›Resting vs active, BMR is a theoretical resting value; wearable TDEE includes continuously estimated movement
- ›Individual variation, all equations have ±10–15% error bands; you are an individual, not a population average
Use the calculated TDEE as a starting estimate and validate against actual weight trends over 2–4 weeks. Track consistently, then adjust.