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BMR & TDEE Calculator
• Uses Mifflin-St Jeor Formula (most accurate)
• Also shows Harris-Benedict Formula
• Calculates BMR and TDEE
• Provides calorie recommendations
• Shows macro nutrient breakdown
Metabolic Assessment Results
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Understanding BMR & TDEE
What is BMR (Basal Metabolic Rate)?
BMR is the number of calories your body needs at rest to maintain basic physiological functions like breathing, circulation, cell production, and nutrient processing. It represents the minimum energy required to sustain life when you're not active. BMR accounts for 60-75% of total daily energy expenditure in sedentary individuals. It's primarily determined by body composition (muscle vs. fat), age, gender, height, and weight.
What is TDEE (Total Daily Energy Expenditure)?
TDEE is the total number of calories your body burns in a day, including BMR plus calories burned through activity (exercise and daily movement). TDEE = BMR × Activity Factor. Understanding your TDEE is essential for managing weight—to lose weight, consume fewer calories than your TDEE; to gain weight, consume more; to maintain, match your TDEE.
BMR Calculation Formulas
| Formula | Accuracy | Description |
|---|---|---|
| Mifflin-St Jeor | Most Accurate (±10%) | Modern formula, accounts for lean body mass. Recommended for most people. More accurate than Harris-Benedict. |
| Harris-Benedict | Accurate (±15%) | Older formula developed in 1919. Still widely used but less accurate than Mifflin-St Jeor, especially for obese individuals. |
| Katch-McArdle | Very Accurate if body fat % known | Uses body fat percentage instead of age. Most accurate if you know your body composition. |
Male: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
Female: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161
TDEE: BMR × Activity Factor
Activity Level Multipliers
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Little or no exercise; desk job or minimal daily activity |
| Lightly Active | 1.375 | Light exercise 1-3 days per week; mostly sedentary job |
| Moderately Active | 1.55 | Moderate exercise 3-5 days per week; active job or regular training |
| Very Active | 1.725 | Intense exercise 6-7 days per week; active job or daily workouts |
| Extremely Active | 1.9 | Physical job; twice daily training; professional athlete |
Factors Affecting BMR
- Muscle Mass: Muscle tissue burns more calories at rest than fat tissue. More muscle = higher BMR
- Age: BMR decreases ~2% per decade after age 30 due to muscle loss
- Gender: Men typically have higher BMR than women due to greater muscle mass
- Body Composition: Higher body fat percentage lowers BMR relative to weight
- Genetics: Heredity accounts for 20-30% of individual BMR variation
- Hormones: Thyroid hormones, cortisol, and other hormones affect metabolism
- Medications: Certain drugs can increase or decrease metabolic rate
- Health Conditions: Thyroid disorders, PCOS, diabetes affect metabolism
- Temperature: Living in cold climates increases BMR; heat adaptation decreases it
Using BMR & TDEE for Your Goals
For Weight Loss
- Caloric Deficit: Consume 300-500 calories below TDEE for sustainable 0.5-1 lb/week loss
- Don't Go Too Low: Consuming below BMR is unsustainable and leads to metabolic slowdown
- Protein Priority: Maintain 0.7-1g protein per lb of body weight to preserve muscle during loss
- Gradual Deficit: A 300-calorie deficit is more sustainable than 500+ calories
- Monitor Progress: Track weight weekly; adjust calories if progress stalls after 2-3 weeks
For Weight Maintenance
- Eat at TDEE: Consume calories equal to your calculated TDEE
- Flexibility: Some days eat slightly above, some below—balance over 1-2 weeks
- Include Exercise: Regular activity (150+ min moderate weekly) supports metabolic health
- Whole Foods: 80% whole foods, 20% flexibility for psychological sustainability
For Weight Gain / Muscle Building
- Caloric Surplus: Consume 300-500 calories above TDEE for 0.5-1 lb/week gain
- High Protein: 1-1.2g protein per lb body weight for optimal muscle growth
- Strength Training: 3-5 days/week resistance training to maximize muscle gain
- Quality Calories: Focus on nutrient-dense foods (whole grains, lean proteins, healthy fats)
- Progressive Overload: Gradually increase training volume for muscle stimulation
Sample Macro Breakdowns
| Goal | Protein | Carbs | Fat | Notes |
|---|---|---|---|---|
| Weight Loss | 30-35% | 40-45% | 20-25% | High protein preserves muscle; moderate carbs for energy |
| Maintenance | 25-30% | 45-50% | 20-25% | Balanced approach for overall health |
| Muscle Gain | 30-35% | 45-50% | 20-25% | High protein for muscle synthesis; adequate carbs for training |
| Athletic | 25-30% | 50-60% | 15-20% | High carbs for performance; adequate protein for recovery |
Frequently Asked Questions about BMR & TDEE
Why do calculators give different BMR results?
Different formulas (Mifflin-St Jeor vs Harris-Benedict) give slightly different results. Mifflin-St Jeor is more modern and accurate. Individual variation can be ±20% regardless of formula.
Does BMR change with age?
Yes. BMR decreases approximately 2% per decade after age 30, primarily due to loss of muscle mass. Strength training helps maintain muscle and preserve BMR.
Can you eat below BMR?
Technically yes, but it's not recommended. Eating consistently below BMR can trigger metabolic adaptation, excessive hunger, and muscle loss. A moderate deficit below TDEE (but above BMR) is better.
How accurate is TDEE calculation?
TDEE estimates are accurate to ±20% at best. Actual needs depend on genetics, metabolism, medications, and other factors. Use calculated TDEE as a starting point and adjust based on real-world results.
Why did my calculated calories change when I input different weight?
Both BMR and TDEE are directly proportional to body weight. As weight increases, calorie needs increase. This is why weight loss gradually reduces daily calorie needs.
Should I use Mifflin-St Jeor or Harris-Benedict?
Use Mifflin-St Jeor—it's more accurate and modern. Harris-Benedict tends to overestimate BMR, especially for obese individuals. However, both are estimates; adjust based on real results.
What if I'm not seeing weight loss on my calculated deficit?
Possible reasons: 1) Underestimating calories consumed, 2) TDEE calculation inaccuracy (±20% variation is normal), 3) Medical conditions affecting metabolism, 4) Insufficient deficit. Adjust by 100-200 calories and reassess after 2-3 weeks.
How often should I recalculate my TDEE?
Recalculate when your weight changes significantly (10+ lbs), your activity level changes, or after 3-4 months if results plateau. Weight loss naturally reduces calorie needs as you have less body mass.
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