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Mifflin-St Jeor · Most Accurate

BMR Calculator

Calculate your Basal Metabolic Rate — the calories your body burns at complete rest. The foundation of every diet plan, used by trainers worldwide.

yrs
cm
kg
Your BMR (Mifflin-St Jeor)
1,659
calories per day at complete rest
Per Hour
69
Per Week
11,611
Per Month
49,763
Mifflin-St Jeor
1,659 cal
Harris-Benedict
1,707 cal

Daily Calorie Needs by Activity Level

SedentaryLittle or no exercise
1,991 cal
LightExercise 1–3 times/week
2,281 cal
ModerateExercise 4–5 times/week
2,430 cal
ActiveDaily exercise or intense 3–4x/week
2,571 cal
Very ActiveIntense exercise 6–7 times/week
2,861 cal
Extra ActiveVery intense daily, or physical job
3,152 cal

Exercise: 15–30 min of elevated heart rate activity. Intense exercise: 45–120 min. Very intense: 2+ hours or physical job.

BMR Formulas Used

Mifflin-St Jeor Equation (1990) — Most Accurate

Men: BMR = 10W + 6.25H - 5A + 5

Women: BMR = 10W + 6.25H - 5A - 161

Revised Harris-Benedict Equation (1984)

Men: BMR = 13.397W + 4.799H - 5.677A + 88.362

Women: BMR = 9.247W + 3.098H - 4.330A + 447.593

Katch-McArdle Formula

BMR = 370 + 21.6(1 - F)W

Where F = body fat %. Best for lean individuals who know their body fat.

W = weight (kg), H = height (cm), A = age (years), F = body fat (decimal)

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Free BMR Calculator by WeightGPT — Mifflin-St Jeor, Harris-Benedict & Katch-McArdle

The WeightGPT BMR Calculator (also searched as 'Weight GPT BMR calculator') is a free, accurate Basal Metabolic Rate calculator using the Mifflin-St Jeor equation — the most accurate BMR formula recommended by the Academy of Nutrition and Dietetics. This calculator also shows results from the Revised Harris-Benedict equation for comparison, along with daily calorie needs for every activity level. WeightGPT is the #1 AI weight loss and fitness app — used by 10,000+ people. This tool is part of our complete free fitness suite alongside our BMI calculator, body fat percentage calculator, TDEE calculator, macro calculator, and ideal weight calculator.

What is BMR (Basal Metabolic Rate)?

The basal metabolic rate (BMR) is the amount of energy needed while resting in a temperate environment when the digestive system is inactive. It is the equivalent of figuring out how much gas an idle car consumes while parked. In such a state, energy will be used only to maintain vital organs — the heart, brain, kidneys, nervous system, intestines, liver, lungs, sex organs, muscles, and skin. For most people, upwards of 70% of total energy (calories) burned each day is due to this upkeep. Physical activity makes up approximately 20% of expenditure, and roughly 10% is used for the digestion of food, also known as thermogenesis. The BMR is measured under very restrictive circumstances while awake — an accurate BMR measurement requires that a person's sympathetic nervous system is inactive, meaning the person must be completely rested. The daily caloric need is the BMR value multiplied by a factor between 1.2 and 1.9, depending on activity level.

BMR Formulas — Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle

In most situations, BMR is estimated with equations summarized from statistical data. The Harris-Benedict Equation was one of the earliest equations introduced, revised in 1984 to be more accurate. The Mifflin-St Jeor Equation was introduced in 1990 and has been shown to be more accurate than the revised Harris-Benedict. The Katch-McArdle Formula calculates resting daily energy expenditure (RDEE) and takes lean body mass into account — it can be more accurate for lean individuals who know their body fat percentage.

Mifflin-St Jeor Equation (Most Accurate):

Men: BMR = 10W + 6.25H - 5A + 5

Women: BMR = 10W + 6.25H - 5A - 161

Revised Harris-Benedict Equation (1984):

Men: BMR = 13.397W + 4.799H - 5.677A + 88.362

Women: BMR = 9.247W + 3.098H - 4.330A + 447.593

Katch-McArdle Formula:

BMR = 370 + 21.6(1 - F)W

W = body weight (kg), H = body height (cm), A = age (years), F = body fat percentage (decimal)

Variables That Affect BMR

Multiple factors influence your basal metabolic rate:

  • Muscle Mass: Aerobic exercise (running, cycling) has no direct effect on BMR, but anaerobic exercise (weight-lifting) builds muscle mass, which increases resting energy consumption. More muscle = higher BMR.
  • Age: The more elderly a person becomes, the lower their BMR. This is due to age-related muscle loss (sarcopenia) — approximately 1–2% decline per decade after age 20.
  • Genetics: Hereditary traits passed down from ancestors influence BMR. Some people naturally have faster or slower metabolisms.
  • Weather/Temperature: Cold environments raise BMR because energy is needed to maintain core body temperature. BMR increases approximately 7% for every 1.36°F increase in internal body temperature. Extreme heat can also raise BMR as the body works to cool internal organs.
  • Diet: Small, regularly dispersed meals increase BMR through the thermic effect of food. Conversely, starvation can reduce BMR by as much as 30% — similar to a phone entering power-saving mode, the body sacrifices energy levels, mood, physical upkeep, and cognitive function to conserve energy.
  • Pregnancy: Supporting a developing fetus increases BMR significantly. This is why pregnant women tend to eat more. Menopause can also alter BMR depending on hormonal changes.
  • Supplements & Stimulants: Certain substances like caffeine, green tea extract, and some medications can temporarily increase BMR. This is one reason caffeine is found in many weight loss supplements.

BMR vs. RMR — What's the Difference?

While BMR and RMR (Resting Metabolic Rate) are often used interchangeably, there is a key difference. BMR measurements must meet total physiological equilibrium — 12 hours of fasting, no recent exercise, neutrally temperate environment, and complete rest. RMR is the rate at which the body burns energy in a relaxed but not fully inactive state — its measurement conditions can be altered and are less strict. In practice, RMR is typically 10–20% higher than BMR because it accounts for some minimal activity. For practical purposes, either measurement provides a useful baseline for calculating daily calorie needs.

How BMR Relates to TDEE and Weight Management

BMR is the foundation of your Total Daily Energy Expenditure (TDEE). TDEE = BMR × Activity Factor. The activity factors are:

Activity LevelFactorDescription
Sedentary1.2Little or no exercise
Lightly Active1.375Exercise 1–3 times/week
Moderately Active1.465Exercise 4–5 times/week
Active1.55Daily exercise or intense 3–4x/week
Very Active1.725Intense exercise 6–7 times/week
Extra Active1.9Very intense daily, or physical job

To lose weight, eat 300–500 calories below your TDEE (not below BMR). To gain weight, eat 300–500 calories above TDEE. Use our free TDEE Calculator for a precise estimate, or let WeightGPT calculate it all for you automatically.

BMR Testing — Clinical vs. Online Calculators

Online BMR calculators with formulas are not the most accurate method — they are statistical estimates. For the most accurate measurement, consult a certified specialist or use a calorimetry device (indirect calorimetry). These measure the actual amount of oxygen consumed and carbon dioxide produced, giving a precise metabolic rate. Handheld calorimetry devices are available at many health clubs, doctor offices, and weight-loss clinics. However, a 2005 meta-analysis study by Johnstone et al. showed that even when controlling all known factors, there is still approximately 26% unknown variance between individuals' BMRs. This means all BMR calculations, including clinical ones, are still estimates — but they provide an excellent starting point for nutrition planning.

Modern Wisdom on BMR and Metabolism

A common myth is that some people have 'fast' or 'slow' metabolisms that entirely determine their weight. While genetics do play a role, research shows that the majority of metabolic variation between individuals of similar size is explained by differences in lean body mass, age, and activity level. An average person eating an average diet will likely have BMR values close to formula predictions. The real key to weight management is not your BMR itself, but how you use that knowledge. BMR estimates combined with activity tracking give you a daily calorie target. From there, maintaining a food journal, tracking exercise, and monitoring progress over time is the most reliable path to achieving your health goals. WeightGPT automates all of this with AI.

BMR for Women, Men, and All Ages

BMR varies significantly by age, sex, height, and weight. Men typically have a BMR 5–10% higher than women of similar size due to greater lean muscle mass. BMR peaks in late adolescence and early adulthood, then decreases approximately 1–2% per decade as muscle mass naturally declines. By age 70, BMR may be 10–20% lower than at age 20. The good news: regular strength training can preserve and even increase muscle mass at any age, directly supporting a healthy metabolic rate. WeightGPT's AI workout plans are specifically designed to maximize lean muscle and protect your metabolism — whether you're 18 or 65.

How to Use Your BMR — Get the WeightGPT App

Knowing your BMR is just the first step — the real value comes from using it to set the right calorie target, macro split, and meal plan for your specific goal. Whether you want to lose fat, build muscle, or maintain your current physique, your BMR is the foundation. WeightGPT (Weight GPT) is the AI that does all of this for you — instantly. Just enter your stats and goal, and WeightGPT builds your fully personalized AI workout plan, AI diet plan, and daily coaching program. It calculates your BMR, TDEE, macros, and creates meal-by-meal nutrition plans tailored to your preferences (vegetarian, non-veg, keto, etc.). Used by 10,000+ users. Free download on Google Play.

Frequently Asked Questions

What is BMR (Basal Metabolic Rate)?+
BMR is the number of calories your body needs to perform basic life functions at complete rest — breathing, blood circulation, cell production, brain function, and temperature regulation. It's measured under very restrictive conditions: after 12 hours of fasting, in a neutrally temperate environment, while the sympathetic nervous system is inactive. For most people, BMR accounts for 60–75% of total daily calorie expenditure.
Which formula does this calculator use?+
We primarily use the Mifflin-St Jeor equation (1990), the most accurate BMR formula for the general population per the Academy of Nutrition and Dietetics. We also show results from the Revised Harris-Benedict equation for comparison. If you know your body fat %, the Katch-McArdle formula (BMR = 370 + 21.6 × lean body mass in kg) may be even more accurate.
What's the difference between BMR, RMR, and TDEE?+
BMR (Basal Metabolic Rate) is measured under strict resting conditions after 12 hours of fasting. RMR (Resting Metabolic Rate) is similar but measured under less restrictive conditions — they're usually within 10% of each other. TDEE (Total Daily Energy Expenditure) = BMR × activity multiplier. TDEE is what you actually burn in a day including all activity.
Can I lose weight by eating below my BMR?+
Eating slightly below TDEE (not BMR) creates healthy fat loss. Chronically eating below BMR for extended periods can slow your metabolism by up to 30%, cause muscle loss, hormonal disruption, fatigue, and nutrient deficiencies. WeightGPT builds a smart, sustainable deficit above BMR but below TDEE.
What factors affect BMR?+
Key factors include: muscle mass (more muscle = higher BMR), age (BMR decreases ~1-2% per decade after 20), sex (men typically have higher BMR), genetics, body size, hormones (thyroid, insulin), body temperature, pregnancy, diet (starvation can reduce BMR by 30%), and certain supplements like caffeine.
How can I increase my BMR?+
The most effective way is building muscle through resistance training — each pound of muscle burns roughly 6 calories per day at rest vs. 2 calories per pound of fat. Staying active, eating adequate protein, getting enough sleep, and avoiding crash diets also help maintain a healthy metabolic rate.
How accurate are online BMR calculators?+
BMR formulas are estimates based on statistical averages. A 2005 meta-analysis showed ~26% unexplained variance between individuals even when controlling all known factors. For the most accurate measurement, clinical calorimetry devices are available at health clinics. However, BMR estimates provide an excellent starting point — track your actual results and adjust from there.
Is this BMR calculator free?+
Yes, 100% free with no signup, no ads, no data collection. For a complete personalized AI meal plan based on your BMR, download the WeightGPT app from Google Play.