What is BMR and how is it different from TDEE?

BMR (Basal Metabolic Rate) is the number of calories your body burns in a 24-hour period while at complete rest — lying still, in a thermoneutral environment, in a post-absorptive state (after 12+ hours of fasting). It represents the minimum energy required to keep your vital organs functioning: brain activity, heart pumping blood, lungs breathing, liver detoxifying, kidneys filtering, and body temperature regulation. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor — it accounts for everything else you do during the day, from walking to the kitchen to running a marathon. TDEE is what you actually burn in a real day. TDEE = BMR × activity multiplier Example: If your BMR is 1,750 kcal/day and you are moderately active (×1.55), your TDEE is 1,750 × 1.55 = 2,713 kcal/day. For nutrition planning: your food intake target is based on TDEE, not BMR. Eating at BMR would be far too low for anyone who is not completely bedridden.

Why do different BMR formulas give different results?

Each formula was derived from a different study population, using different measurement methods and time periods: • Mifflin-St Jeor (1990): Derived from 498 men and women; validated against measured BMR using indirect calorimetry in normal-weight, overweight, and obese subjects. Most current and accurate for general population. Mean error ~10%. • Harris-Benedict (originally 1919, revised 1984): Original study had only 239 subjects and used respiratory calorimetry. The Roza & Shizgal (1984) revision updated the coefficients. Tends to overestimate by ~5% in sedentary individuals. • Katch-McArdle: Derived from lean body mass measurements, not total weight. This is why it is more accurate for muscular people (whose extra weight is muscle, not fat) and less accurate when body fat is unknown. • Owen (1986–87): Published in two papers (male/female separately). Very simple weight-only formula — ignores height and age. More accurate across a wider weight range than expected, but loses the age-related decline component. • Schofield (1985): Developed for the WHO/FAO. Based on a large meta-analysis of 7,173 subjects from multiple countries. Uses weight and age-band coefficients, without height (which makes it simpler but slightly less precise than Mifflin for individuals). In practice, all five formulas agree within ~100–150 kcal/day for most adults of average height and weight. The differences become more pronounced at height or weight extremes.

Which organs use the most energy at rest?

The body's resting energy expenditure is dominated by a small number of metabolically active organs — not muscles: Organ-level BMR distribution (approximate, per Elia 1992): • Liver: ~27% of BMR — metabolically the most active organ per kg • Brain: ~19% of BMR — only ~2% of body weight but very energy-hungry • Skeletal muscle (at rest): ~18% of BMR — large total mass, but relatively low per-kg activity at rest • Kidneys: ~10% of BMR — continuous filtration is energetically expensive • Heart: ~7% of BMR — never stops contracting; ~5 watts of continuous power • Other organs + tissues: ~19% of BMR Key insight: The brain and liver together account for ~46% of your entire BMR despite making up only ~3–4% of body weight. This is why starvation diets cause cognitive impairment — the brain gets priority for available glucose. Muscle mass matters most for long-term metabolism: while muscle has low per-kg BMR at rest, it accounts for 70–80% of active energy expenditure. This is why gaining muscle increases TDEE significantly, even if the BMR impact is more modest.

How does BMR change with age?

BMR naturally declines with age, primarily due to loss of lean mass (sarcopenia — age-related muscle loss). The decline begins around age 25–30 and accelerates after 60. Rate of decline: • Ages 20–50: approximately 1–2% per decade (roughly 20–30 kcal/decade at average weight) • Ages 50–80: accelerates to ~3–4% per decade as muscle loss increases • Overall: roughly 100–150 kcal/day lower at age 60 vs age 20 for the same body weight However, body weight also typically increases with age, which partially offsets BMR decline. When studies control for lean mass, much of the apparent BMR decline disappears — suggesting that maintaining muscle mass is the single most effective way to preserve metabolic rate with age. What you can do: • Resistance training (2–4× per week): most effective intervention to preserve lean mass and BMR • Adequate protein (1.2–1.6g/kg/day): prevents muscle breakdown during energy restriction • Avoid extreme calorie restriction: causes disproportionate muscle loss and accelerates BMR decline

Can I increase my BMR?

BMR is largely determined by genetics, body size, and composition — but several factors genuinely raise it: 1. Build muscle (most effective): Each kg of additional muscle tissue burns approximately 10–13 kcal/day at rest. Gaining 5 kg of muscle raises BMR by ~50–65 kcal/day permanently. This is the most sustainable way to elevate metabolic rate. 2. Avoid crash dieting: Severe calorie restriction triggers metabolic adaptation — BMR can drop 10–15% below formula predictions. This is why very-low-calorie diets cause weight loss plateaus. 3. Thyroid function: The thyroid gland controls metabolic rate. Hypothyroidism (underactive thyroid) can reduce BMR by 20–40%. If you consistently eat less than your calculated BMR without losing weight, thyroid function is worth investigating with a doctor. 4. Caffeine and stimulants: Provide a modest, temporary BMR boost of ~3–11% for a few hours. Not meaningful for long-term metabolism. 5. Cold exposure: Shivering and non-shivering thermogenesis temporarily increase energy expenditure. Brown adipose tissue (BAT) is involved. Not practically significant for most people. 6. Protein-rich diet: The thermic effect of protein (20–30% of protein calories lost as heat during digestion) increases daily energy expenditure by 80–100 kcal on a high-protein diet.

Why is my BMR different from what I expected?

Several factors can make your calculated BMR differ from expectations: 1. High muscle mass: Formula BMR is based on total weight, not muscle. A very muscular person weighing 90 kg has a higher true BMR than the formula predicts, because muscle is metabolically active. Use Katch-McArdle with your body fat % for more accurate results. 2. High fat mass ('skinny fat'): Conversely, someone with high body fat relative to weight has a lower true BMR than formulas predict, since fat tissue burns very few calories at rest (~4.5 kcal/kg/day vs ~13 kcal/kg/day for muscle). 3. Thyroid conditions: Hypothyroidism reduces BMR significantly; hyperthyroidism raises it. 4. Chronic calorie restriction: Long-term dieting adapts your metabolism below formula predictions. This is metabolic adaptation — real, measurable, and well-documented. 5. Formula choice: Different formulas can give results up to 150–200 kcal/day apart for the same person, particularly at weight or height extremes. The most accurate approach: rather than relying solely on any formula, track your actual food intake for 2–3 weeks at a stable weight, then average daily calories. That is your true TDEE — and BMR is typically 60–75% of it.

BMR Calculator — Basal Metabolic Rate

The BMR Calculator computes your Basal Metabolic Rate — the calories your body burns each day at complete rest — using all five major scientific formulas simultaneously: Mifflin-St Jeor (most accurate, recommended by AND), Harris-Benedict Revised (1984), Katch-McArdle (best for athletes who know body fat %), Owen (1986..

YOUR DETAILS

WEIGHT (kg)

HEIGHT

= 5ft 8.9in

AGE (years)

yrs

BMR FORMULA

YOUR BMR

BASAL METABOLIC RATE

1,749

kcal/day — calories burned at complete rest

PER HOUR

72.9

kcal/hour

PER MINUTE

1.21

kcal/min

AVERAGE (ALL FORMULAS)

1,766

kcal/day

ALL FORMULAS

Mifflin

1,749

Harris

1,830

Katch

1,787

Owen

1,695

Schofield

1,791

FORMULA COMPARISON (kcal/day)

WHERE YOUR BMR CALORIES GO (organ energy use)

BMR DECLINE WITH AGE (kcal/day)

BMR declines ~5 kcal/year from age 20–70 for this profile

TDEE BY ACTIVITY LEVEL

Sedentary×1.2

2,099 kcal

Lightly Active×1.375

2,405 kcal

Moderately Active×1.55

2,711 kcal

Very Active×1.725

3,017 kcal

Extremely Active×1.9

3,323 kcal

For a full calorie plan with goal calories and macro targets, use the TDEE Calculator →

Created with❤️byeaglecalculator.com

HOW TO USE

1
Select your unit system (Metric or Imperial) and biological sex. Then enter your current weight, height, and age. These three values are the inputs for the four height-and-weight-based BMR formulas (Mifflin-St Jeor, Harris-Benedict, Owen, Schofield). Use your actual body weight — not a goal weight — for an accurate baseline.
2
Choose a BMR formula. Mifflin-St Jeor is selected by default — it is the most validated formula for the general population and what the Academy of Nutrition and Dietetics recommends. Harris-Benedict (Revised 1984) is the classic clinical formula and gives similar results. Owen (1987) is the simplest — it uses weight only, with no height or age. Schofield (WHO 1985) uses age-stratified coefficients and is used in clinical and public health nutrition globally. Katch-McArdle is the most accurate for athletes and muscular individuals because it uses lean body mass instead of total weight.
3
If you selected Katch-McArdle, enter your body fat percentage to unlock it. Lean mass is calculated automatically as weight × (1 − BF%/100). You can use the Body Fat Percentage calculator on this site to measure your BF% using the US Navy method if you do not have a recent measurement.
4
Read your results: the large number is your BMR in kcal/day — the calories your body burns at complete rest just to keep organs functioning. Below it you see BMR per hour and per minute. The formula comparison bar chart shows all five formula results side by side so you can see the spread and choose the most appropriate one for your profile.
5
Explore the visualisers: the organ breakdown donut chart shows where your BMR calories go — the liver alone uses ~27%, the brain ~19%, resting muscle ~18%, kidneys ~10%, heart ~7%. The BMR-vs-age line chart shows how your BMR would decline from age 20 to 70 at your current weight and height — approximately 5 kcal/year for an average adult. The TDEE table shows your estimated maintenance calories at each of the five activity levels.

WORKED EXAMPLE

BMR calculation for a 30-year-old male, 80 kg, 175 cm: MIFFLIN-ST JEOR: BMR = 10×80 + 6.25×175 − 5×30 + 5 BMR = 800 + 1093.75 − 150 + 5 = 1,749 kcal/day HARRIS-BENEDICT (Revised): BMR = 88.362 + 13.397×80 + 4.799×175 − 5.677×30 BMR = 88.362 + 1071.76 + 839.825 − 170.31 = 1,830 kcal/day KATCH-MCARDLE (assuming 18% body fat, lean mass = 65.6 kg): BMR = 370 + 21.6 × 65.6 = 370 + 1416.96 = 1,787 kcal/day OWEN (male): BMR = 879 + 10.2 × 80 = 879 + 816 = 1,695 kcal/day SCHOFIELD (30–59 age band, male): BMR = 11.472 × 80 + 873.1 = 917.76 + 873.1 = 1,791 kcal/day Average of all 5: (1749 + 1830 + 1787 + 1695 + 1791) / 5 = 1,770 kcal/day Per hour: 1,749 / 24 = 72.9 kcal/hr Per minute: 1,749 / 1440 = 1.21 kcal/min ORGAN BREAKDOWN (using Mifflin BMR of 1,749 kcal): • Liver (27%): 472 kcal/day • Brain (19%): 332 kcal/day • Resting muscles (18%): 315 kcal/day • Kidneys (10%): 175 kcal/day • Heart (7%): 122 kcal/day • Other (19%): 332 kcal/day TDEE ESTIMATES (Mifflin BMR 1,749 kcal): • Sedentary (×1.2): 2,099 kcal/day • Lightly Active (×1.375): 2,405 kcal/day • Moderately Active (×1.55): 2,711 kcal/day • Very Active (×1.725): 3,017 kcal/day • Extremely Active (×1.9): 3,323 kcal/day

REFERENCE FORMULAS

FORMULA REFERENCE TABLE

Name	Formula	Description
Mifflin-St Jeor — Male	BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5	Published 1990. Most accurate for general population. Recommended by AND. Error ~10%.
Mifflin-St Jeor — Female	BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161	Lower constant (−161 vs +5) reflects lower average lean mass relative to total weight.
Harris-Benedict — Male	BMR = 88.362 + 13.397×kg + 4.799×cm − 5.677×age	Revised by Roza & Shizgal (1984). Overestimates ~5% for sedentary individuals.
Harris-Benedict — Female	BMR = 447.593 + 9.247×kg + 3.098×cm − 4.330×age	Original: Harris & Benedict (1919); revised constants from Roza & Shizgal (1984).
Katch-McArdle	BMR = 370 + 21.6 × lean mass(kg)	Only formula using lean body mass. Best for athletes. Requires known body fat %.
Lean mass (for Katch)	Lean = weight × (1 − BF% / 100)	Input to Katch-McArdle. Use body fat calculator or DEXA scan for best accuracy.
Owen — Male	BMR = 879 + 10.2 × weight(kg)	Owen et al. (1986). Weight-only formula. No height or age. Simpler but less accurate.
Owen — Female	BMR = 795 + 7.18 × weight(kg)	Owen et al. (1987). Female version with lower slope coefficient.
Schofield — Male 18–29	BMR = 15.057×kg + 692.2	WHO (1985) Schofield equation. Age-stratified — different coefficients per age band.
Schofield — Male 30–59	BMR = 11.472×kg + 873.1	Used in clinical nutrition and public health settings globally.
Schofield — Female 18–29	BMR = 14.818×kg + 486.6	Weight-only per age group; does not include height.
BMR per hour	kcal/hr = BMR / 24	Divide daily BMR by 24 to get hourly resting calorie burn.

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Last updated: April 29, 2026 · Formulas: Mifflin-St Jeor (1990), Harris-Benedict revised (1984), Katch-McArdle, Owen (1986–87), Schofield/WHO (1985) · Eagle-eyed accuracy for every calculation.