Calculate your Basal Metabolic Rate — the calories your body burns at rest — using the most accurate formulas available. The foundation of all calorie and nutrition planning.
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic physiological functions — breathing, circulating blood, regulating temperature, growing and repairing cells, and keeping every organ functioning. It represents the absolute minimum energy requirement to keep you alive if you lay completely still in a climate-controlled environment for 24 hours, neither digesting food nor moving a muscle.
BMR is the foundation of all calorie calculations in nutrition science. Every estimate of daily calorie needs starts with BMR, then adds energy expenditure from activity, digestion, and other factors. Get BMR wrong, and every downstream calculation — weight loss targets, muscle building goals, maintenance calories — is wrong too. This is why choosing the right formula and inputting accurate measurements matters so much.
For most people, BMR accounts for 60–75% of total daily calorie expenditure. Even on a completely sedentary day, the overwhelming majority of calories burned come from your body simply keeping itself alive. This has important implications for weight management: crash diets that dramatically cut calories don't slow you down because you're not exercising less — they slow you down because your body actually lowers its BMR in response to severe calorie restriction, burning fewer calories at rest to preserve energy.
BMR vs RMR vs TDEE: What's the Difference?
BMR (Basal Metabolic Rate) is measured under strict laboratory conditions — fasted state, completely rested, thermally neutral environment. It's the most restrictive definition of resting metabolism. RMR (Resting Metabolic Rate) is similar but measured under less strict conditions — typically after a period of rest but not necessarily fully fasted. RMR is about 10–20% higher than BMR for most people and is what most online calculators actually estimate when they say "BMR." TDEE (Total Daily Energy Expenditure) is your total calorie burn including all activity — BMR plus exercise, digestion (the thermic effect of food), and non-exercise activity thermogenesis (NEAT: fidgeting, walking around, daily tasks).
Metric
What It Measures
Typical % of TDEE
Your Control
BMR / RMR
Calories at complete rest
60–75%
Low (age, genetics, muscle mass)
NEAT
Non-exercise daily movement
15–30%
Medium (posture, fidgeting, steps)
Exercise (EAT)
Deliberate workouts
5–10%
High
TEF
Digesting food
8–12%
Low–Medium (protein raises it)
TDEE
Total daily burn
100%
Variable
💡 NEAT Is Underrated: Non-Exercise Activity Thermogenesis (NEAT) — all the movement you do that isn't deliberate exercise — can vary by up to 2,000 calories per day between individuals of the same size. A naturally fidgety person who walks to meetings, takes the stairs, and stands at their desk may burn 500–1,000 more calories daily than a sedentary person of the same weight and workout frequency. Increasing NEAT (10,000 steps per day, a standing desk, walking phone calls) is often more impactful for weight management than adding exercise sessions.
BMR Formulas: Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle
Three formulas dominate BMR estimation in clinical and fitness settings. They use different inputs and were validated on different populations, which is why they sometimes produce meaningfully different results — especially for individuals who are significantly above or below average body composition.
Mifflin-St Jeor Formula (Most Accurate for Most People)
Developed in 1990, the Mifflin-St Jeor equation is widely considered the most accurate formula for estimating RMR in the general population. The American Dietetic Association recommends it as the preferred method for estimating calorie needs. It's validated across a wide range of ages and body types, making it the default choice for most calorie calculators.
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Studies show the Mifflin-St Jeor formula predicts measured RMR within 10% for approximately 82% of people — significantly better than the Harris-Benedict formula it largely replaced.
Harris-Benedict Formula (Revised 1984)
The original Harris-Benedict equation was published in 1919 — one of the earliest systematic attempts to quantify human metabolism. The revised version (Roza and Shizgal, 1984) improved accuracy and remains widely used. It tends to slightly overestimate BMR, particularly in obese individuals.
Men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age)
Women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age)
Katch-McArdle Formula (Best When Body Fat % Is Known)
The Katch-McArdle formula is unique in that it uses lean body mass (weight minus fat mass) rather than total body weight. This makes it the most accurate formula for people who know their body fat percentage — particularly athletes and individuals with unusually high or low body fat levels. Muscle is metabolically active tissue; fat is largely inert. Two people of identical weight but very different body compositions (one lean athlete, one sedentary person with high body fat) have very different BMRs, and only the Katch-McArdle formula captures this distinction.
All sexes: BMR = 370 + (21.6 × lean body mass in kg)
If your body fat percentage is known and you're outside the average range — either very lean (under 15% for men, under 22% for women) or carrying significant excess body fat — the Katch-McArdle formula will give you a more accurate BMR than either weight-based formula.
💡 Which Formula Should You Use? For most people without a reliable body fat percentage measurement, Mifflin-St Jeor is the best choice — it's the most extensively validated and recommended by dietitians. If you have an accurate body fat percentage (from a DEXA scan, hydrostatic weighing, or reliable BIA device), use Katch-McArdle. Harris-Benedict is still useful as a cross-check or when comparing historical calculations. The Formula Compare tab above shows all three results simultaneously so you can see the range and use the average as a conservative estimate.
What Affects Your BMR? Factors You Can and Cannot Control
BMR is not fixed. It changes throughout your life in response to age, body composition changes, hormonal fluctuations, and even dietary patterns. Understanding which factors affect your BMR — and which direction they push it — gives you a much more sophisticated understanding of weight management than simple calorie counting.
Factors That Raise BMR
Muscle mass. Muscle tissue burns approximately 6 calories per pound per day at rest, compared to about 2 calories per pound for fat tissue. This is why strength training is so effective for long-term weight management — every pound of muscle added raises your daily calorie burn even on rest days.
Height. Taller people have more body surface area and greater organ mass, requiring more energy at rest.
Pregnancy. Growing a fetus significantly increases metabolic demands, raising BMR by 15–25% in the third trimester.
Cold exposure. Your body burns significantly more calories maintaining core temperature in cold environments — one reason cold weather athletes have elevated metabolisms.
Hyperthyroidism. An overactive thyroid dramatically accelerates metabolism, sometimes raising BMR by 50–100%.
Factors That Lower BMR
Age. BMR typically declines 1–2% per decade after age 20, primarily due to loss of muscle mass (sarcopenia). This is why maintaining strength training into middle age and beyond is critically important for metabolic health.
Severe calorie restriction. Eating dramatically below your BMR triggers metabolic adaptation — your body actively lowers its resting metabolic rate to preserve energy. This is the mechanism behind "starvation mode" and why very low calorie diets plateau quickly.
Hypothyroidism. An underactive thyroid slows metabolism significantly and is a common cause of unexplained weight gain.
Loss of muscle mass. Whether from aging, inactivity, or crash dieting, losing muscle mass directly reduces BMR. Crash diets that cause rapid weight loss destroy muscle alongside fat, permanently reducing the dieter's resting metabolic rate.
Age Group
Avg Male BMR
Avg Female BMR
Key Change
18–25
1,800–2,000
1,400–1,600
Peak metabolic rate
26–35
1,750–1,950
1,350–1,550
Gradual decline begins
36–45
1,700–1,900
1,300–1,500
Muscle loss accelerates
46–55
1,620–1,820
1,250–1,450
Hormonal changes (menopause)
56–65
1,550–1,750
1,200–1,400
Significant sarcopenia risk
65+
1,400–1,650
1,150–1,350
Major muscle preservation priority
Frequently Asked Questions
Should I eat below my BMR to lose weight?
Eating below your BMR is generally not recommended and can be counterproductive. Your BMR represents the minimum calories needed for basic survival functions — eating below it consistently signals to your body that it's in a famine state, triggering metabolic adaptation (your body lowers its BMR to conserve energy), muscle breakdown for fuel, hormonal disruption, nutrient deficiencies, and fatigue. The recommended approach is to calculate your TDEE based on your activity level, then create a moderate deficit of 250–500 calories per day from that number. This produces sustainable weight loss of 0.5–1 lb per week without triggering the metabolic defense mechanisms that make extreme restriction self-defeating. See our Calorie Deficit Calculator and TDEE Calculator for precise targets.
Why is my BMR different from what I expected?
BMR calculators produce estimates based on population-level formulas — they're highly accurate on average but can vary from your actual metabolic rate by 10–15% in either direction. The most common reasons for unexpected results include: body composition that differs significantly from the population average (very muscular or very high body fat percentage), a thyroid condition affecting metabolic rate, measurement errors in height or weight, or age-related muscle loss that isn't captured by weight-based formulas. For the most accurate personalized BMR, a metabolic cart test (indirect calorimetry) performed at a sports medicine clinic or research facility measures your actual oxygen consumption and gives a direct BMR measurement rather than an estimate.
How can I increase my BMR?
The most effective and sustainable ways to raise BMR are: building muscle mass through progressive resistance training (each pound of muscle burns approximately 6 calories per day at rest), eating adequate protein (protein has the highest thermic effect of any macronutrient — roughly 25–30% of protein calories are burned during digestion), getting sufficient sleep (sleep deprivation measurably reduces BMR and increases hunger hormones), and avoiding extreme calorie restriction that triggers metabolic adaptation. Cardio exercise burns calories during the workout but has minimal impact on resting BMR. Strength training is the only reliable way to meaningfully increase your BMR long-term by increasing metabolically active muscle tissue.
How is BMR different from TDEE?
BMR is the calories burned at complete rest — your body's baseline energy demand. TDEE (Total Daily Energy Expenditure) includes your BMR plus all additional calories burned through physical activity (exercise and daily movement), digestion (thermic effect of food), and other factors. TDEE is what actually matters for nutrition planning because it represents the calories you actually burn on a typical day. For a sedentary person, TDEE is roughly 1.2× BMR. For a moderately active person, it's about 1.55× BMR. For a very active athlete, it can be 1.9× BMR or higher. Always plan your calorie intake based on TDEE, not BMR. Use our TDEE Calculator for your complete daily energy expenditure.
Does BMR change with weight loss?
Yes — BMR decreases as you lose weight, for two reasons. First, a smaller body simply requires fewer calories to maintain at rest. Second, if weight loss includes muscle loss (as is common with rapid weight loss), the metabolic cost of that muscle is gone. This is why weight loss tends to plateau: as you lose weight, your BMR drops, so the same calorie deficit becomes smaller relative to your new, lower TDEE. Recalculating your BMR and TDEE every 10–15 pounds of weight lost is good practice. Preserving muscle through resistance training and adequate protein intake (~0.7–1g per pound of body weight) minimizes the BMR reduction that accompanies weight loss.
Is BMR the same for men and women?
No — men typically have a higher BMR than women of the same age, height, and weight, primarily because men naturally carry more muscle mass and less fat mass. On average, men have 10–15% higher BMR than women of equivalent body size. Hormonal differences also play a role: testosterone promotes muscle growth and slightly elevates metabolic rate, while estrogen does not have the same effect. After menopause, when estrogen levels drop dramatically, many women experience an acceleration in the age-related decline of muscle mass and BMR — another reason strength training becomes especially important for women in their 40s and beyond.