BMR Calculator — Basal Metabolic Rate
Calculate your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest. Compares 3 scientifically validated formulas: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle. See also TDEE Calculator and Calorie Calculator.
Enables Katch-McArdle formula
What is Basal Metabolic Rate (BMR)?
Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions at complete rest — breathing, blood circulation, cell production, nutrient processing, and maintaining body temperature. BMR accounts for approximately 60-75% of your total daily calorie expenditure. Even if you stayed in bed all day without moving, your body would still burn this many calories just to keep you alive. Understanding your BMR is the foundation for any nutrition plan, whether your goal is weight loss, muscle gain, or maintenance.
BMR vs TDEE vs RMR — What is the Difference?
BMR (Basal Metabolic Rate)
Calories burned at absolute rest in a neutrally temperate environment, after 12 hours of fasting and 8 hours of sleep. Measured in strict clinical conditions. This is the minimum energy your body needs to survive.
RMR (Resting Metabolic Rate)
Similar to BMR but measured under less strict conditions (no fasting requirement). RMR is typically 10-20% higher than BMR. Most online calculators (including this one) actually estimate RMR, though they label it BMR.
TDEE (Total Daily Energy Expenditure)
Your total calories burned per day including all activity. TDEE = BMR x Activity Multiplier. This is the number you actually use for diet planning. Use our TDEE Calculator for a detailed breakdown.
BMR Formulas Explained
This calculator uses three scientifically validated equations. Each has different strengths:
1. Mifflin-St Jeor Equation (1990) — Recommended
Men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
Recommended by the Academy of Nutrition and Dietetics as the most accurate for most people. Best for general population with normal to overweight BMI.
2. Harris-Benedict Equation (Revised 1984)
Men: BMR = 88.362 + (13.397 x weight kg) + (4.799 x height cm) - (5.677 x age)
Women: BMR = 447.593 + (9.247 x weight kg) + (3.098 x height cm) - (4.330 x age)
The original 1919 equation revised by Roza and Shizgal in 1984. Tends to overestimate by 5-15% compared to Mifflin-St Jeor, especially for overweight individuals.
3. Katch-McArdle Equation (1996)
BMR = 370 + (21.6 x Lean Body Mass in kg)
Lean Body Mass = Weight x (1 - Body Fat % / 100)
Most accurate for lean/athletic individuals because it accounts for muscle mass. Requires knowing your body fat percentage. Use our Body Fat Calculator to estimate yours.
Example BMR Calculation
30-year-old male, 75 kg, 178 cm, 18% body fat
Mifflin-St Jeor:
BMR = (10 x 75) + (6.25 x 178) - (5 x 30) + 5
BMR = 750 + 1112.5 - 150 + 5 = 1,718 cal/day
Harris-Benedict (Revised):
BMR = 88.362 + (13.397 x 75) + (4.799 x 178) - (5.677 x 30)
BMR = 88.362 + 1004.775 + 854.222 - 170.31 = 1,777 cal/day
Katch-McArdle:
Lean Mass = 75 x (1 - 0.18) = 61.5 kg
BMR = 370 + (21.6 x 61.5) = 1,698 cal/day
Factors That Affect Your BMR
Muscle Mass
Muscle tissue burns more calories at rest than fat tissue. Each pound of muscle burns approximately 6 calories/day at rest vs 2 calories/day for fat. This is why strength training increases BMR over time.
Age
BMR decreases approximately 1-2% per decade after age 20, primarily due to loss of muscle mass (sarcopenia). A 50-year-old typically has a BMR 100-200 calories lower than a 25-year-old of the same size.
Gender
Men typically have 5-10% higher BMR than women of the same weight due to higher muscle mass and lower body fat percentage. Hormonal differences (testosterone vs estrogen) also play a role.
Genetics & Thyroid Function
Thyroid hormones (T3, T4) directly regulate metabolic rate. Hypothyroidism can reduce BMR by 15-40%. Genetic variation accounts for approximately 200-300 calorie differences between individuals of the same size.
Diet & Caloric Restriction
Prolonged caloric restriction (crash dieting) can reduce BMR by 15-20% through metabolic adaptation. This is why extreme diets often lead to weight regain. Gradual calorie reduction (250-500 cal deficit) minimizes this effect.
How to Increase Your BMR
1. Build muscle through strength training: Each kg of muscle gained increases BMR by approximately 13 calories/day. Over time, this compounds significantly. Aim for 2-3 strength sessions per week.
2. Eat enough protein: Protein has the highest thermic effect of food (TEF) — your body burns 20-30% of protein calories just digesting it, compared to 5-10% for carbs and 0-3% for fat. Aim for 1.6-2.2g per kg of body weight.
3. Avoid crash diets: Severe caloric restriction triggers metabolic adaptation, lowering your BMR. Stick to a moderate deficit (250-500 calories below TDEE) to preserve metabolic rate.
4. Stay hydrated: Studies show that drinking 500ml of cold water can temporarily boost metabolism by 24-30% for about an hour as your body heats the water to body temperature.
5. Get adequate sleep: Sleep deprivation (less than 7 hours) can reduce BMR by 5-20% and increase hunger hormones (ghrelin), making weight management harder.
6. High-Intensity Interval Training (HIIT): HIIT creates an afterburn effect (EPOC) that elevates metabolism for 24-48 hours post-exercise, effectively increasing your average daily BMR.
BMR Reference Table by Age and Gender
| Age | Male (75kg, 178cm) | Female (60kg, 165cm) |
|---|---|---|
| 18 | 1,768 cal | 1,387 cal |
| 25 | 1,733 cal | 1,352 cal |
| 30 | 1,708 cal | 1,327 cal |
| 35 | 1,683 cal | 1,302 cal |
| 40 | 1,658 cal | 1,277 cal |
| 45 | 1,633 cal | 1,252 cal |
| 50 | 1,608 cal | 1,227 cal |
| 55 | 1,583 cal | 1,202 cal |
| 60 | 1,558 cal | 1,177 cal |
| 65 | 1,533 cal | 1,152 cal |
* Calculated using Mifflin-St Jeor equation
Frequently Asked Questions
Which BMR formula is most accurate?
The Mifflin-St Jeor equation (1990) is recommended by the Academy of Nutrition and Dietetics as the most accurate for most people. However, if you know your body fat percentage, the Katch-McArdle formula is more accurate for lean/athletic individuals because it accounts for muscle mass directly.
Why do the three formulas give different results?
Each formula was developed using different study populations and variables. Harris-Benedict (1919/1984) tends to overestimate for overweight people. Mifflin-St Jeor uses a more modern dataset. Katch-McArdle ignores age/gender entirely and uses only lean mass, making it best for athletes but requiring body fat data.
How do I use BMR for weight loss?
First, calculate your TDEE (BMR x activity multiplier). To lose weight, eat 250-500 calories below your TDEE. Never eat below your BMR — this triggers metabolic adaptation and muscle loss. A 500 cal/day deficit equals approximately 0.45 kg (1 lb) of fat loss per week.
Can I eat below my BMR?
Eating below your BMR is not recommended for extended periods. It can cause metabolic adaptation (your body lowers its BMR to conserve energy), muscle loss, nutrient deficiencies, hormonal disruption, and fatigue. Always aim to eat at least your BMR, even when cutting.
Does exercise increase BMR?
Yes, but primarily through building muscle mass (long-term effect). Each kg of muscle increases BMR by about 13 cal/day. HIIT also creates a temporary BMR increase (EPOC) lasting 24-48 hours. Cardio alone has minimal long-term BMR impact unless it builds muscle.
Why does BMR decrease with age?
Primarily due to sarcopenia — the natural loss of muscle mass with aging (3-8% per decade after 30). Hormonal changes (declining testosterone, growth hormone, and thyroid function) also contribute. Strength training can significantly slow this decline.
How accurate are BMR calculators?
Online BMR calculators are estimates with a typical accuracy of plus or minus 10%. The gold standard for measuring BMR is indirect calorimetry (measuring oxygen consumption), which requires clinical equipment. For most people, calculator estimates are sufficient for diet planning — just monitor your weight over 2-3 weeks and adjust calories if needed.