Activity Level

Daily Calories (TDEE)

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Published by MetaSys Limited · Page updated 19 September 2026 · Editorial policy. Educational information; not a medical review.

BMR vs. TDEE: Understanding Your Calorie Baseline

Your Basal Metabolic Rate (BMR) is the number of calories your body burns each day just to maintain basic physiological functions while at complete rest — no movement, no digestion, nothing. It covers the energy cost of breathing, circulating blood, regulating body temperature, repairing cells, and running your brain and organs. For most adults, BMR accounts for 60–75% of total daily calorie expenditure, making it the single largest component of your energy budget.

How the Mifflin-St Jeor Equation Works

Our BMR calculator uses the Mifflin-St Jeor equation, developed in 1990 and a published equation for estimating resting energy expenditure. The equation incorporates your weight, height, age, and sex. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. The reason men have a higher BMR than women of equivalent size and age is primarily due to greater average muscle mass — muscle tissue is metabolically active and burns more calories at rest than fat tissue.

BMR vs. TDEE: What Is the Difference?

BMR and TDEE are often used interchangeably but they are distinct numbers. BMR assumes you are lying completely still in a thermoneutral environment, post-absorptive (not digesting food). TDEE (Total Daily Energy Expenditure) adds all the calories burned through physical activity, walking, the thermic effect of food (digesting and processing what you eat — roughly 10% of total calories), and non-exercise activity thermogenesis (NEAT — all the small movements you make throughout the day). For most people, TDEE is 1.3 to 1.9 times their BMR, depending on how active they are.

What Affects Your BMR?

Several factors influence your BMR beyond the inputs in this calculator. Muscle mass is the biggest driver — each pound of muscle burns roughly 6–10 calories per day at rest, while fat tissue burns only 2–3. This is why resistance training is the most effective long-term strategy for raising metabolism. Age decreases BMR by roughly 1–2% per decade after 20, largely due to gradual muscle loss (sarcopenia). Hormones — particularly thyroid hormones — regulate metabolic rate significantly; hypothyroidism can lower BMR by 30–40%. Genetics accounts for a variance of roughly 200–400 calories between individuals of the same body composition.

How to Use Your BMR in Practice

Your BMR is your floor — you should never eat below this number without medical supervision, because doing so deprives your body of the calories needed for basic organ function. Use it as the foundation for calculating your TDEE: multiply your BMR by the appropriate activity factor (shown in the table above) to find your maintenance calories. From there, you can create a calorie deficit or surplus based on your goals. If your TDEE comes out lower than expected, consider whether your activity level estimate is accurate and whether your muscle mass might be lower than average.

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BMR Calculator — Frequently Asked Questions

What is a normal BMR for an adult?

BMR varies widely based on body size, composition, age, and sex. For an average adult woman (5'5", 140 lbs, age 35), BMR is roughly 1,350–1,450 calories per day. For an average adult man (5'10", 180 lbs, age 35), BMR is roughly 1,750–1,900 calories per day. Taller, heavier, more muscular individuals have higher BMRs. The range across the healthy adult population spans from about 1,200 to 2,200+ calories per day.

Can I increase my BMR?

Yes, and the most effective way is building muscle mass through progressive resistance training. Since muscle tissue burns more calories at rest than fat tissue, increasing your muscle-to-fat ratio directly raises your BMR over time. Eating adequate protein supports muscle retention and also has a high thermic effect — your body burns about 25–30% of protein calories just in the process of digesting it. Getting enough sleep is also critical; poor sleep elevates cortisol, promotes fat storage, and impairs the hormonal signaling needed for muscle protein synthesis.

Does BMR slow down during dieting?

Yes — this is called adaptive thermogenesis, and it's a well-documented response to caloric restriction. When you eat in a deficit over time, your body reduces its energy expenditure beyond what weight loss alone would predict, as a survival mechanism. Studies suggest this adaptation can reduce daily calorie burn by 100–300 calories. It's a key reason why aggressive, prolonged calorie restriction tends to produce diminishing returns. Periodic diet breaks (eating at maintenance for 1–2 weeks) and resistance training to preserve muscle mass are the best strategies to minimize this adaptation.

Which BMR formula is most accurate — Mifflin-St Jeor or Harris-Benedict?

Multiple validation studies have found the Mifflin-St Jeor equation to be the most accurate predictive equation for BMR in healthy adults, particularly for people who are overweight. The Harris-Benedict equation (developed in 1919 and revised in 1984) tends to overestimate BMR by about 5% in obese individuals. The Katch-McArdle equation, which incorporates lean body mass, can be more accurate if you know your body fat percentage. For most people without a DEXA scan, Mifflin-St Jeor is the best available tool, which is why we use it here.

Should I ever eat below my BMR?

In almost all cases, no. Eating below your BMR means your body doesn't have enough calories to run its basic organ functions — this leads to rapid muscle breakdown, nutritional deficiencies, hormonal disruption, hair loss, fatigue, and impaired immune function. The only circumstances where sub-BMR calorie intake is appropriate are very-low-calorie medical programs (under 800 cal/day using specially formulated meal replacements) supervised by physicians, typically for patients with severe obesity where the risks of rapid weight loss are outweighed by the risks of continued obesity.

BMR Calculator