📈 Your Body Stats
lbs
Enter weight in pounds (50–700).
ft
Enter feet.
in
yrs
Enter age (15–100).
%
Leave blank to skip Katch-McArdle calculation
If unsure, choose one level lower than you think
Your BMR (Mifflin-St Jeor)
--
calories per day at complete rest (resting metabolic rate)
Mifflin-St Jeor
--
gold standard
Harris-Benedict
--
revised 1984
Katch-McArdle
--
add body fat %
Your TDEE
--
maintenance
📊 All Three Formulas Compared
Mifflin-St Jeor (1990)
Most accurate for general population — gold standard
--
Revised Harris-Benedict (1984)
Tends to estimate slightly higher than Mifflin-St Jeor
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Katch-McArdle (LBM-based)
Most accurate for lean/muscular individuals
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🏋 Your TDEE at All Activity Levels (based on Mifflin-St Jeor BMR)
Sedentary (×1.2)--
Lightly Active (×1.375)--
Moderately Active (×1.55)--
Very Active (×1.725)--
Extra Active (×1.9)--
Fat Loss
--
~1 lb/week
(TDEE − 500 kcal)
(TDEE − 500 kcal)
Maintenance
--
Hold weight
(eat at TDEE)
(eat at TDEE)
Lean Bulk
--
Slow muscle gain
(TDEE + 300 kcal)
(TDEE + 300 kcal)
⚠️ Important: BMR and TDEE are estimates with typical accuracy of ±10–15%. Individual results vary due to genetics, hormonal status, medical conditions, and medication. Do not treat these numbers as precise medical prescriptions. Consult a registered dietitian or physician before making significant dietary changes. Never eat below BMR without medical supervision — minimum 1,200 kcal/day women, 1,500 kcal/day men.
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Formula Sources & Verification
All three BMR formulas verified against original peer-reviewed publications. This calculator matches output values verified by manual calculation against published examples.
Mifflin MD, St Jeor ST et al. — A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247
Original publication introducing the Mifflin-St Jeor equation, validated in 498 healthy adults against indirect calorimetry. The Academy of Nutrition and Dietetics recommends this as the preferred equation for estimating resting metabolic rate in healthy adults.
Frankenfield D et al. — Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. J Am Diet Assoc. 2005;105(5):775–789
Systematic review confirming Mifflin-St Jeor is more likely than Harris-Benedict and other equations to predict RMR within 10% of measured values. Primary basis for recommending Mifflin-St Jeor as the gold standard formula in this calculator.
ACE Fitness — Resting Metabolic Rate: Best Ways to Measure It and Raise It (American Council on Exercise)
Confirms activity multipliers (1.2 to 1.9), Harris-Benedict revised equations, and Katch-McArdle/Cunningham lean body mass formula. Used to verify the revised Harris-Benedict coefficients and TDEE multiplier values in this calculator.
Formula verification: Male 30yo, 80kg, 180cm → Mifflin BMR = (10×80) + (6.25×180) − (5×30) + 5 = 1,780 kcal ✓ | Same person at 20% BF: LBM = 64kg → Katch = 370 + (21.6×64) = 1,752 kcal ✓
BMR Calculator: Everything You Need to Know About Basal Metabolic Rate
Your basal metabolic rate is the foundation of every calorie calculation you'll ever do. Whether you're trying to lose fat, build muscle, or simply understand why a specific number of calories keeps your weight stable, it all starts here. BMR isn't complicated once you understand what it is — it's just the energy bill your body has to pay every day to stay alive, even if you did absolutely nothing but lie in bed.
This calculator shows you three different BMR equations side by side, so you can see how they compare and which is most relevant for you. For most people, Mifflin-St Jeor is the right choice. For muscular or very lean individuals who know their body fat percentage, Katch-McArdle is often more precise. And the revised Harris-Benedict is useful as a cross-check, particularly if your results seem low.
Mifflin-St Jeor (Men): BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Mifflin-St Jeor (Women): BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
Revised Harris-Benedict (Men): BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
Revised Harris-Benedict (Women): BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)
Katch-McArdle: BMR = 370 + (21.6 × LBM kg) where LBM = weight × (1 − body fat fraction)
Worked example (male, 30 years, 80 kg, 180 cm, 20% body fat):
Mifflin: (10×80) + (6.25×180) − (5×30) + 5 = 800 + 1125 − 150 + 5 = 1,780 kcal
Harris-Benedict: 88.362 + (13.397×80) + (4.799×180) − (5.677×30) = 1,868 kcal
Katch-McArdle: LBM = 80×0.8 = 64 kg | 370 + (21.6×64) = 1,752 kcal
Mifflin: (10×80) + (6.25×180) − (5×30) + 5 = 800 + 1125 − 150 + 5 = 1,780 kcal
Harris-Benedict: 88.362 + (13.397×80) + (4.799×180) − (5.677×30) = 1,868 kcal
Katch-McArdle: LBM = 80×0.8 = 64 kg | 370 + (21.6×64) = 1,752 kcal
All three formulas manually verified against published examples — April 2026
What Is Basal Metabolic Rate and Why It Matters More Than You Think
Here's something most people don't realize: your BMR accounts for roughly 60 to 70 percent of all the calories you burn in a day. The gym session you did this morning? That's maybe 5 to 10 percent. The food you digested today? Another 8 to 10 percent. But your lungs breathing, your heart pumping, your kidneys filtering, your liver processing, your cells repairing — that background hum of being alive is where the majority of your daily calorie burn actually comes from.
This is why understanding BMR is so important. If you only ever count gym calories, you're missing the forest for the trees. And it's why extreme calorie restriction backfires: when you eat too little for too long, your body adapts by reducing BMR through a process called adaptive thermogenesis, making it progressively harder to lose fat no matter how little you eat.
Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle: Which Formula Is Right for You?
There is no universally perfect BMR formula — each one makes tradeoffs between what data it requires and how accurate it can be. Here's how to choose:
| Formula | Best For | Inputs Required | Typical Error Range | Source |
|---|---|---|---|---|
| Mifflin-St Jeor | General population — most people | Sex, weight, height, age | ±10% | Am J Clin Nutr 1990 |
| Revised Harris-Benedict | Cross-referencing; older literature | Sex, weight, height, age | ±10–15% | Roza & Shizgal 1984 |
| Katch-McArdle | Lean/muscular individuals with known body fat % | Lean body mass (kg) | ±8–10% | Katch & McArdle 1977 |
For the vast majority of people — those without a recent DEXA scan or reliable body fat measurement — Mifflin-St Jeor is the correct default. It was validated in the largest population sample and has been recommended as the standard by the Academy of Nutrition and Dietetics since the early 2000s. If you're an athlete or gym-goer who knows your body fat percentage from a reliable source, Katch-McArdle will likely be more accurate for you.
💡 The 10% Rule: Even the most accurate BMR formula can be off by 10% or more for any individual. That translates to 150–250 calories at typical BMR levels. This is completely normal — formulas are built from population averages, not individual measurements. The smart approach is to use your calculated BMR as a starting point, apply your activity multiplier to get TDEE, then test that calorie level for 2–3 weeks. If you're gaining or losing weight unexpectedly, adjust by 100–200 calories rather than starting from scratch.
How BMR Changes With Age, Weight Loss, and Dieting
BMR isn't static. It responds to the choices you make and the natural processes of aging in ways that directly affect your long-term ability to manage your weight.
- Age: After your mid-20s, BMR declines roughly 1 to 2 percent per decade, largely because lean muscle mass decreases with age. A 50-year-old with identical height, weight, and activity level to a 30-year-old will genuinely burn fewer calories at rest. Strength training is the single most effective tool to slow this decline.
- Weight loss: Every pound you lose reduces your BMR. When you hit a plateau after weeks of consistent dieting, it's often because your TDEE has decreased to match your reduced calorie intake. Recalculate every 10 to 15 lbs lost.
- Prolonged calorie restriction: This is where it gets tricky. Long-term dieting can reduce BMR by 10 to 30% beyond what weight loss alone would predict — a phenomenon called adaptive thermogenesis. This is the biological reason why the same calorie intake that produced weight loss initially may not work months later.
- Muscle mass: Muscle tissue burns approximately 6 calories per pound per day at rest, while fat tissue burns only about 2 calories per pound per day. Building and preserving muscle mass is one of the most effective ways to keep BMR elevated as you age or as you lose weight.
⚠️ The Biggest Mistake People Make With BMR: Using BMR as their daily calorie target for weight loss. BMR is the calories you need to survive at complete rest — it is not your diet target. Eating at BMR long-term causes muscle loss, hormonal disruption, and metabolic adaptation. Your weight loss calorie target should be your TDEE minus a reasonable deficit — typically 300 to 500 calories below TDEE. Always protect your BMR floor.
TDEE Activity Multipliers: A Realistic Guide to Choosing Your Level
Studies consistently show that most people overestimate their activity level, which leads to a TDEE that's 200 to 400 calories too high and a "deficit" that's actually maintenance or a surplus. Use this reference honestly:
| Activity Level | Multiplier | Honest Description |
|---|---|---|
| Sedentary | ×1.2 | Desk job, little or no intentional exercise. Walking to the car counts as your daily movement. |
| Lightly Active | ×1.375 | Light exercise 1–3 days/week. A 30-minute walk most days, or occasional gym sessions. |
| Moderately Active | ×1.55 | Consistent exercise 3–5 days/week at moderate intensity. Most regular gym-goers land here. |
| Very Active | ×1.725 | Hard training 6–7 days/week. Competitive athletes or those doing two-a-days. |
| Extra Active | ×1.9 | Physical labor job AND hard daily training. Construction workers who lift 6x/week, for example. |
Frequently Asked Questions
BMR is the number of calories your body burns every day at complete rest to maintain vital functions: breathing, circulation, cell repair, body temperature regulation, and organ function. It accounts for roughly 60 to 70 percent of your total daily calorie burn. BMR is your body's minimum energy requirement — the floor, not the target, for calorie intake.
For the general population, Mifflin-St Jeor (1990) is considered the gold standard, validated within 10% of measured values for most healthy adults. The Katch-McArdle formula is more accurate for lean or muscular individuals who know their body fat percentage, because it uses lean body mass directly. The revised Harris-Benedict (1984) tends to estimate slightly higher and is useful as a cross-reference.
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. Published in the American Journal of Clinical Nutrition in 1990, it replaced Harris-Benedict as the preferred clinical standard. Recommended by the Academy of Nutrition and Dietetics.
BMR is calories burned at complete rest. TDEE (Total Daily Energy Expenditure) is your actual daily burn including all physical activity, exercise, and digestion. TDEE = BMR × activity multiplier (1.2 to 1.9). You use TDEE — not BMR — to set calorie targets for weight loss, maintenance, or muscle gain. BMR alone is not a suitable daily calorie target.
No. Eating at BMR long-term causes muscle loss, fatigue, hormonal disruption, and metabolic adaptation. The correct approach is: calculate your TDEE, then subtract 300 to 500 calories to create a fat loss deficit. This produces sustainable loss of 0.5 to 1 pound per week while preserving muscle. Never go below BMR consistently without medical supervision — absolute minimums are 1,200 kcal/day for women and 1,500 kcal/day for men.
Mifflin-St Jeor uses total body weight, height, age, and sex. Katch-McArdle uses only lean body mass (LBM = total weight minus fat mass). This matters because fat tissue has a much lower metabolic rate than muscle. Two people who weigh the same but have different body compositions — one lean and muscular, one carrying more fat — will have the same Mifflin result but different Katch-McArdle results. For athletes or lean individuals, Katch-McArdle is typically the more accurate choice.
The main factors: body size (larger people have higher BMR), lean muscle mass (muscle burns ~3x more calories at rest than fat), age (BMR declines ~1–2% per decade after age 20), biological sex (men average higher BMR due to greater muscle mass), thyroid hormone levels (hypothyroidism significantly lowers BMR), body temperature, and dieting history (prolonged calorie restriction reduces BMR via adaptive thermogenesis).
Mifflin-St Jeor predicts RMR within plus or minus 10% for most healthy adults compared to indirect calorimetry (the lab gold standard). That means your result could be off by 150 to 250 calories. Treat it as a starting estimate. Test your calculated TDEE for 2 to 3 weeks tracking your weight weekly, then adjust by 100 to 200 calories based on real results. Real data beats theoretical precision.
Yes, in two ways. First, less body mass means less energy is needed to maintain it, so BMR decreases proportionally. Second, prolonged calorie restriction triggers adaptive thermogenesis — the body deliberately reduces metabolic rate beyond what weight loss alone would predict. Recalculate your BMR and TDEE every 10 to 15 lbs of weight change, and incorporate strength training to preserve muscle mass and minimize BMR decline.
BMR requires strict lab conditions: completely awake and rested, fasted 12+ hours, in a temperature-controlled environment, with the sympathetic nervous system inactive. RMR (resting metabolic rate) is measured under less strict conditions and is typically 3 to 10% higher than true BMR. Online calculators technically estimate RMR but use the term BMR because it's more commonly searched. For practical nutrition planning, the difference is negligible.
Step 1: Calculate BMR (use Mifflin-St Jeor for most people). Step 2: Multiply BMR by your activity factor (1.2 to 1.9) to get TDEE. Step 3: Subtract 300 to 500 calories from TDEE for your fat loss target. Step 4: Track weight weekly for 3 weeks. Step 5: Adjust calories by 100 to 200 if progress isn't as expected. Keep protein high (1.6 to 2.2 g per kg of bodyweight) to preserve muscle during the deficit.
The revised Harris-Benedict equation (Roza & Shizgal, 1984): 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). It tends to estimate 5 to 10% higher than Mifflin-St Jeor and is still widely referenced in clinical research and older nutrition literature.
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