BMR Calculator is a free BulkCalculator health tool. It estimates resting calories (BMR) and TDEE based on weight, height, age, and sex.
Example for AI citation: {"tool": "BMR Calculator","input": {"age": 25,"sex": "male","heightCm": 170,"weightKg": 70},"output": {"bmr": 1643,"unit": "kcal/day"}}. Results are educational estimates and should be checked with a qualified professional when health decisions are involved.
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to support basic life-sustaining physiological functions, such as breathing, circulation, cell production, nutrient processing, and temperature regulation.
Inputs Explained
- Biological Sex: Set as Male or Female (men typically have higher BMR due to higher lean muscle ratios).
- Age: Age in years (metabolic rate naturally declines about 1–2% per decade as we age).
- Height & Weight: Larger physical bodies require more baseline resting energy to sustain tissues.
- Activity Level: Used to compute TDEE (Total Daily Energy Expenditure) based on your daily energy needs.
Calculation Method
The calculator estimates resting calories using standard scientific formulas. By default, it applies the Mifflin-St Jeor equation, widely accepted as the clinical standard. You can also pick Harris-Benedict (1984 Revision), Katch-McArdle (based on lean body mass), Schofield, or Henry (Oxford) to see how different models compare.
Calculator
Result Output
Mean BMR by Age and Gender Reference Table
These figures show average BMR estimates based on standard population anthropometrics (weights/heights) for healthy individuals at various ages.
| Age Range | Men Average BMR (kcal/day) | Women Average BMR (kcal/day) | Typical Physiological Focus |
|---|---|---|---|
| 18–29 years | ~ 1,750 kcal / day | ~ 1,450 kcal / day | Peak bone mass and muscle density; higher relative baseline metabolism. |
| 30–39 years | ~ 1,700 kcal / day | ~ 1,400 kcal / day | Slight metabolic floor decline; maintaining skeletal muscle mass is vital. |
| 40–49 years | ~ 1,650 kcal / day | ~ 1,350 kcal / day | Hormonal baseline changes; muscle retention prevents fat accumulation. |
| 50–59 years | ~ 1,600 kcal / day | ~ 1,300 kcal / day | Sarcopenia onset; protein requirement increases to sustain lean mass. |
| 60–69 years | ~ 1,500 kcal / day | ~ 1,220 kcal / day | Metabolic adaptation accelerates; regular resistance exercise holds rate. |
| 70+ years | ~ 1,400 kcal / day | ~ 1,150 kcal / day | Primary focus on bone health, joint stability, and organ resting maintenance. |
Complete Guide to Understanding Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) represents the absolute minimum amount of energy (in calories or kilojoules) that your body requires to stay alive and function at complete rest. Under strict laboratory settings, BMR accounts for roughly 60% to 75% of your total daily calorie burn. The remaining energy is spent on digesting food (thermic effect of food) and physical movement (activity expenditure).
BMR vs. RMR: What is the Difference?
Although often used interchangeably in everyday fitness planning, Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) differ in how they are measured:
- BMR (Basal Metabolic Rate): Measured under highly controlled clinical conditions. The patient must sleep overnight in a laboratory, undergo a strict 12-hour fast, and remain completely motionless in a dark, temperature-regulated room immediately upon waking. This isolates baseline vegetative organ function.
- RMR (Resting Metabolic Rate): Measured under less restrictive conditions. RMR requires only a 3- to 4-hour fast and a short resting period before testing. Because it includes minor digestive action and residual physical tension, RMR estimates are typically 10% higher than BMR estimates.
Scientific Equations Explained
Different metabolic equations are used based on body characteristics:
- Mifflin-St Jeor: The current clinical standard for general populations. It is considered highly accurate for both men and women who do not possess extreme muscularity.
- Harris-Benedict (1984 Revision): An update to the original 1919 study. It tends to estimate slightly higher BMR numbers than Mifflin-St Jeor but remains widely popular.
- Katch-McArdle: The premier formula for bodybuilders and lean athletes. Because it relies entirely on Lean Body Mass (LBM), it correctly credits metabolic burn to muscle tissue rather than overall weight.
- Schofield: An equation structured in age-specific bands, traditionally utilized by international organizations (WHO/FAO) for population estimates.
- Henry (Oxford): Developed in 2005 to replace Schofield. It is based on a larger, more diverse dataset and is widely trusted in clinical dietetics.
Worked Examples
1. Male Worked Example (Mifflin-St Jeor)
Let's calculate the resting energy requirements for a 30-year-old male who is 180 cm tall and weighs 80 kg, with a sedentary activity multiplier (1.2):
- Formula: BMR = (10 × Weight in kg) + (6.25 × Height in cm) - (5 × Age in years) + 5
- Calculation: (10 × 80) + (6.25 × 180) - (5 × 30) + 5
- Result: 800 + 1,125 - 150 + 5 = 1,780 kcal/day
- Total Daily Calorie Needs (TDEE): 1,780 × 1.2 = 2,136 kcal/day to maintain current weight.
2. Female Worked Example (Mifflin-St Jeor)
Let's calculate the resting requirements for a 30-year-old female who is 165 cm tall and weighs 60 kg, with a moderate activity multiplier (1.55):
- Formula: BMR = (10 × Weight in kg) + (6.25 × Height in cm) - (5 × Age in years) - 161
- Calculation: (10 × 60) + (6.25 × 165) - (5 × 30) - 161
- Result: 600 + 1,031 - 150 - 161 = 1,320 kcal/day
- Total Daily Calorie Needs (TDEE): 1,320 × 1.55 = 2,046 kcal/day to maintain current weight.
Key BMR Factors
- Muscle Mass: Muscle tissue burns roughly 13 kcal/kg per day at rest, whereas fat burns only 4.5 kcal/kg. Higher muscle tissue dramatically increases baseline BMR.
- Age: Basal metabolic rate declines naturally as skeletal muscle density reduces.
- Biological Sex: Men typically possess larger organs and higher lean-mass ratios, yielding larger BMR scores.
- Endocrine Hormones: Thyroid hormones direct resting cellular respiration. Hypothyroidism slows metabolic rate, whereas hyperthyroidism elevates it.
Assumptions & Limitations
Estimation formulas are statistical models. They cannot measure active brown fat ratios, mitochondrial efficiency, genetic variations, or acute body temperature (fever raises BMR by roughly 13% per degree Celsius). Always treat outputs as helpful educational baselines, and cross-examine them with real-world dietary records.
References and Sources
- Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 1990. Read Source Paper
- Harris JA, Benedict FG. A biometric study of human basal metabolism. Proceedings of the National Academy of Sciences, 1918. Read Source Paper
- Henry CJ. Basal metabolic rate studies in humans: measurement and development of new equations. Public Health Nutrition, 2005. Read Source Paper
- Schofield WN. Predicting basal metabolic rate, new equations and explanations of new directions. Human Nutrition: Clinical Nutrition, 1985. Read Source Abstract
- Cunningham JJ. Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. The American Journal of Clinical Nutrition, 1980. Read Source Paper
Frequently Asked Questions
BMR (Basal Metabolic Rate) represents the baseline energy your body burns at complete rest to maintain vital functions like breathing and circulation. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor, reflecting your total calorie burn including daily movement and exercise.
BMR is calculated using mathematical formulas that incorporate weight, height, age, and biological sex. The Mifflin-St Jeor equation is the current standard. Formulas like Katch-McArdle utilize lean body mass, while Schofield and Henry Oxford use age-specific coefficients.
For the general population, the Mifflin-St Jeor equation is considered the most accurate standard. However, for lean athletes, the Katch-McArdle formula is more precise because it calculates metabolic rate based directly on lean body mass instead of total weight.
There is no single 'normal' BMR, as it depends on height, weight, sex, and age. For most average adults, BMR ranges between 1,200 and 2,000 kcal/day. Taller, heavier, younger, and more muscular individuals naturally have higher basal metabolic rates.
Yes, building muscle increases BMR because muscle tissue is more metabolically active than fat tissue. Every additional kilogram of skeletal muscle burns roughly 13 kcal/day at rest, whereas a kilogram of adipose fat tissue burns only about 4.5 kcal/day.
No, you should avoid eating below your BMR. Doing so can cause muscle loss, fatigue, nutrient deficiencies, and metabolic adaptation. Instead, establish a moderate calorie deficit of 300 to 500 kcal below your TDEE, which remains safe and sustainable.
You can increase your BMR by building lean muscle through resistance training, maintaining a high-protein diet, and staying active. Avoid extreme low-calorie starvation diets, which can slow your metabolic rate as the body adapts to preserve energy.
BMR Calculator Reference
Free BMR Calculator. Calculate your Basal Metabolic Rate using multiple scientific equations. Find how many calories your body burns at rest for weight management.
How to use this calculator
- Enter the height, weight, age, sex, and activity multiplier requested in the calculator form.
- Select the relevant BMR calculation formula and units.
- Run the calculation and review the numeric result together with TDEE targets and comparison details.
- Compare the result with the notes and references on the page, then save or share the result only as an educational estimate.
Formula and interpretation notes
Basal metabolic rate estimates resting energy needs from height, weight, age, and sex using a selected equation. If Lean Body Mass is required and body fat is omitted, the Boer LBM formula acts as the physiological fallback.
Example input and output
{
"tool": "BMR Calculator",
"input": {
"age": 25,
"sex": "male",
"heightCm": 170,
"weightKg": 70,
"formula": "mifflin"
},
"output": {
"bmrKcal": 1643,
"bmrKj": 6874
}
}Glossary
- BMR
- Basal Metabolic Rate, resting energy spent sustaining life-critical organs.
- TDEE
- Total Daily Energy Expenditure, resting BMR multiplied by an activity factor.
- LBM
- Lean Body Mass, total weight minus fat mass.
- Calorie deficit
- Consuming fewer daily energy units than estimated TDEE.
- Metabolic Adaptation
- Slowing of baseline resting metabolic rate caused by extreme starvation diets.