BMR vs TDEE Explained: What's the Difference?

If you've ever used a calorie calculator, you've probably encountered two acronyms: BMR and TDEE. These two numbers are fundamental to understanding your body's energy needs, yet many people confuse them or don't understand how they relate to weight management.

In this article, we'll demystify both concepts, explain the science behind them, and show you how to use this knowledge for effective weight loss, maintenance, or muscle gain.

What is BMR (Basal Metabolic Rate)?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain vital functions. Think of it as the "base operating cost" of running your body — the energy needed just to keep you alive if you stayed in bed all day without moving.

BMR accounts for essential processes like:

• Breathing: Your respiratory system runs 24/7
• Heart function: Pumping blood throughout your body
• Brain activity: Your brain uses about 20% of your daily energy
• Cell production: Constantly replacing old cells with new ones
• Temperature regulation: Maintaining your core body temperature at 37°C
• Organ function: Liver, kidneys, and other organs working around the clock

For most people, BMR accounts for 60-75% of total daily calorie expenditure. This means the majority of calories you burn each day goes toward basic survival, not exercise or movement.

Factors That Affect BMR

Your BMR is influenced by several factors, some of which you can control and others you cannot:

• Age: BMR decreases by about 2% per decade after age 20
• Sex: Men typically have higher BMR due to greater muscle mass
• Weight and height: Larger bodies require more energy to maintain
• Body composition: Muscle burns more calories at rest than fat
• Genetics: Some people naturally have faster or slower metabolisms
• Hormones: Thyroid function significantly impacts metabolism
• Temperature: Cold environments can increase BMR

What is TDEE (Total Daily Energy Expenditure)?

Your Total Daily Energy Expenditure (TDEE) is the total number of calories you burn in a 24-hour period. It includes your BMR plus all additional energy used for movement, exercise, and digestion.

TDEE is calculated as:

TDEE is made up of four components:

1. BMR (60-75%): Basal metabolic rate as explained above
2. NEAT (15-30%): Non-Exercise Activity Thermogenesis — all non-exercise movement like walking, fidgeting, standing, household chores
3. TEF (10%): Thermic Effect of Food — energy used to digest, absorb, and process food
4. EAT (5-10%): Exercise Activity Thermogenesis — intentional exercise like gym workouts, running, sports

BMR vs TDEE: A Side-by-Side Comparison

How to Calculate Your BMR

Several equations exist for estimating BMR. The most commonly used and generally most accurate for healthy adults is the Mifflin-St Jeor equation, published in 1990:

Example calculation: A 35-year-old woman who is 165cm tall and weighs 70kg would have a BMR of approximately:

(10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 700 + 1031.25 − 175 − 161 = 1,395 calories

How to Calculate Your TDEE

Once you have your BMR, multiply it by an activity factor to estimate TDEE:

Using our example above, a lightly active woman with a BMR of 1,395 would have a TDEE of approximately 1,395 × 1.375 = 1,918 calories per day.

Using BMR and TDEE for Weight Management

For Weight Loss

To lose weight, you need to eat fewer calories than your TDEE (not your BMR). The NHS recommends a deficit of approximately 500-600 calories per day for sustainable weight loss of 0.5-1kg per week.

Important: You should generally not eat below your BMR without medical supervision. Eating too few calories can:

• Slow your metabolism
• Cause muscle loss
• Lead to nutrient deficiencies
• Trigger binge eating
• Disrupt hormonal balance

For Weight Maintenance

To maintain your current weight, eat roughly equal to your TDEE. Your weight will naturally fluctuate day-to-day due to water retention, so focus on weekly averages rather than daily weights.

For Weight Gain (Muscle Building)

To gain weight (primarily muscle with proper training), eat above your TDEE. A surplus of 250-500 calories per day, combined with strength training, supports muscle growth while minimising fat gain.

Common Misconceptions

Myth: "I should eat my BMR to lose weight"

Reality: Eating at BMR is usually too aggressive for sustainable weight loss. If your BMR is 1,400 and your TDEE is 2,000, eating 1,400 calories creates a 600-calorie deficit — fine for some people, but this leaves no margin for error and may be too restrictive for others.

Myth: "Exercise is the main way to boost TDEE"

Reality: NEAT (daily movement) often contributes more to TDEE than formal exercise. Focusing on staying active throughout the day — walking, standing, taking stairs — can boost your calorie burn more than occasional gym sessions.

Myth: "Eating less will always help me lose weight"

Reality: Eating too little can backfire. Very low calorie diets can cause metabolic adaptation, where your body lowers its energy expenditure to conserve calories. This makes weight loss harder and regain easier.

Conclusion

Understanding the difference between BMR and TDEE is essential for effective weight management. Your BMR tells you the minimum calories your body needs to function; your TDEE tells you how many calories you actually burn each day.

For most people, TDEE is the more useful number. It's the baseline from which you calculate your calorie target — subtract 500-600 for weight loss, match it for maintenance, or add 250-500 for muscle gain.

Remember that all calculations are estimates. Use them as starting points, then adjust based on your real-world results over 2-4 weeks.