What Is Your Basal Metabolic Rate (BMR)?

BMR and TDEE: The Two Numbers Behind Weight Management

Basal Metabolic Rate (BMR) is the number of calories your body requires at complete rest to maintain basic physiological functions: breathing, circulation, cell repair, hormone regulation, and temperature maintenance. It represents your baseline energy expenditure — what you would burn lying still for 24 hours without eating, moving, or doing anything. BMR typically accounts for 60-75% of total daily calorie expenditure.

Total Daily Energy Expenditure (TDEE) is BMR multiplied by an activity factor — the total calories your body uses on an average day given your actual activity level. TDEE is the number you need to know for weight management: eat at TDEE to maintain weight, below TDEE to lose fat, above TDEE to gain muscle mass. The quality and accuracy of your TDEE estimate determines how well any diet or fitness program works.

The most widely used BMR formulas are the Mifflin-St Jeor equation (most accurate for most adults) and the Harris-Benedict equation (older, slightly less accurate but still widely cited). For lean individuals with known body fat percentage, the Katch-McArdle formula — which uses lean mass rather than total weight — provides even better accuracy, because muscle burns more calories at rest than fat.

Calculate your BMR and TDEE

Enter your age, sex, height, weight, and activity level to find your BMR and total daily calorie needs for maintaining, losing, or gaining weight.

Calculate My BMR

How to Calculate and Use Your BMR

1
Calculate BMR using the Mifflin-St Jeor equation
For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161. Example: 35-year-old woman, 68 kg, 165 cm: BMR = (10 × 68) + (6.25 × 165) − (5 × 35) − 161 = 680 + 1031.25 − 175 − 161 = 1375 calories/day.
2
Apply your realistic activity multiplier
Sedentary (desk job, minimal exercise): ×1.2. Lightly active (light exercise 1-3 days/week): ×1.375. Moderately active (moderate exercise 3-5 days/week): ×1.55. Very active (hard exercise 6-7 days/week): ×1.725. Extra active (physical job plus hard exercise or twice-daily training): ×1.9. Multiply your BMR by the appropriate factor to get TDEE. For the example above with light activity (×1.375): TDEE = 1,375 × 1.375 = 1,891 calories/day.
3
Set your calorie target based on your goal
Maintain weight: eat at TDEE. Lose fat (0.5-1 lb/week): eat 250-500 calories below TDEE. Lose fat aggressively (1-2 lbs/week): eat 500-1,000 calories below TDEE. Gain lean mass: eat 200-400 calories above TDEE. Never eat below your BMR for extended periods — this signals starvation to your body and causes disproportionate muscle loss alongside fat loss.
4
Validate with 2-3 weeks of real data
Track food intake accurately for 2-3 weeks at your calculated TDEE while tracking weight daily (use weekly averages to smooth out daily fluctuations). If you are gaining weight at calculated TDEE, your actual TDEE is lower — reduce by 100-150 calories. If losing weight at calculated TDEE, your actual TDEE is higher. Use the real data to calibrate rather than relying solely on the formula.
5
Adjust for changes in weight and activity over time
BMR is not fixed. Significant weight loss or gain changes BMR (less weight means lower BMR). Major changes in activity level change TDEE. As you lose weight, your TDEE decreases — this is why calorie targets that worked at the start of a diet become less effective over months. Recalculate BMR and TDEE every 10-15 lbs of weight change, or whenever your activity level significantly changes.

Frequently Asked Questions

Why does BMR decrease as you age?

BMR decreases with age primarily due to declining lean muscle mass (sarcopenia), which begins in the 30s and accelerates after 60. Muscle tissue is metabolically active and burns calories at rest; fat tissue burns very few calories. A 60-year-old with the same weight as a 30-year-old typically has less muscle mass and more fat, resulting in lower BMR. Resistance training throughout adulthood is the most effective intervention against age-related BMR decline.

What is the difference between BMR and RMR?

Basal Metabolic Rate (BMR) is measured under strict conditions: fasted for 12 hours, fully rested, in a thermoneutral environment, lying completely still. Resting Metabolic Rate (RMR) is measured under less strict conditions — typically fasted for only 4-5 hours, at rest but not requiring complete temperature or position controls. RMR is approximately 10-20% higher than BMR. Most online calculators actually estimate RMR rather than true BMR, though the terms are often used interchangeably.

Does eating more meals increase metabolism?

No. The 'eat more frequent meals to boost metabolism' claim is not supported by research. The thermic effect of food (calories burned digesting food) depends on total caloric intake and macronutrient composition, not meal frequency. Eating 2,000 calories in 3 meals burns essentially the same number of calories through digestion as eating the same 2,000 calories in 6 meals. Meal frequency is a preference issue, not a metabolism issue.

How much does muscle vs fat affect BMR?

Muscle tissue burns approximately 6-7 calories per pound per day at rest; fat tissue burns approximately 2 calories per pound per day. Replacing 10 lbs of fat with 10 lbs of muscle increases BMR by approximately 40-50 calories/day. This is real but modest — the metabolic advantage of muscle is often overstated. The more significant practical implication: maintaining muscle mass during weight loss prevents disproportionate BMR decline.

Can you significantly boost your metabolic rate?

Within limits. Resistance training builds muscle mass, which modestly increases BMR over time. High-intensity exercise creates a post-exercise oxygen consumption (EPOC) effect that elevates metabolism for hours after exercise. Adequate protein intake (1.6-2.2 g/kg/day) maximizes the thermic effect of food (protein has a 25-30% thermic effect versus 5-10% for carbohydrates and 0-3% for fat). Dramatic 'metabolism boosting' claims from supplements or special diets are not supported by evidence.

Should I eat back calories burned during exercise?

When using a TDEE that includes your exercise in the activity multiplier (which most TDEE calculators do), you should not eat back exercise calories — they are already accounted for. If you are using a sedentary TDEE and tracking exercise calories separately through a fitness device, you would add those calories to your daily target. The most common error: using a high activity multiplier TDEE and still eating back exercise calories, creating a significant surplus.

Calculate your BMR and daily calorie target

Find your maintenance calories and set the right deficit or surplus for your specific goal.