BMR & TDEE Calculator

Understanding BMR and TDEE: Your Complete Energy Expenditure Guide

Your metabolism is the engine that powers every function in your body — from breathing and blood circulation to cellular repair and physical movement. Understanding how many calories you burn each day is the most fundamental step in any weight management or fitness plan. This calculator provides two essential metrics: your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE), giving you the data foundation for informed nutrition decisions.

What is Basal Metabolic Rate (BMR)?

BMR represents the minimum energy your body needs to maintain vital functions while at complete rest — breathing, blood circulation, cell production, brain function, temperature regulation, and organ maintenance. For most people it is the largest part of daily energy expenditure, often about 60–70%. Key factors include body size and lean mass (each kg of muscle uses roughly 13 kcal/day at rest vs about 4.5 for fat), age (resting expenditure tends to fall gradually, largely with loss of lean mass), sex (men are higher on average, mainly because of more lean mass), genetics and hormonal status such as thyroid function.

The Mifflin-St Jeor Equation

Our calculator uses the Mifflin-St Jeor equation (1990). A systematic review in the Journal of the American Dietetic Association (Frankenfield et al., 2005) found it predicted resting metabolic rate within 10% of measured values in more people than the other equations studied — but it still missed by more than 10% in a substantial minority. Strictly, it estimates resting metabolic rate (RMR), which is close to but slightly above true BMR.

Formula: men = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5; women = the same − 161. Worked example: a 30-year-old man, 70 kg, 175 cm: 10 × 70 + 6.25 × 175 − 5 × 30 + 5 ≈ 1,649 kcal BMR. With "Moderate" activity (×1.55), TDEE ≈ 1,648.75 × 1.55 ≈ 2,556 kcal/day. The calculator rounds the displayed values to whole calories.

What is Total Daily Energy Expenditure (TDEE)?

TDEE is your BMR plus all additional calories burned through three components: the Thermic Effect of Food (TEF, approximately 10% of calorie intake, representing energy used to digest food), Non-Exercise Activity Thermogenesis (NEAT, including walking, fidgeting, standing, and household activities), and Exercise Activity Thermogenesis (EAT, formal workout sessions). Together, TDEE represents what you actually burn in a 24-hour period. To maintain weight, eat approximately your TDEE. For weight loss, eat below it. For muscle gain, eat above it.

Choosing Your Activity Level Accurately

The activity multiplier is a large source of error in TDEE estimates, and many people overestimate their activity. The calculator's levels are: Sedentary (×1.2) — desk job, little or no exercise. Light (×1.375) — exercise 1–3 days per week. Moderate (×1.55) — exercise 3–5 days per week. Active (×1.725) — exercise 6–7 days per week. Very Active (×1.9) — hard daily exercise or a physical job plus training. These are traditional, widely used approximations, not measured values. When in doubt, choose a lower level and adjust based on your weight trend over 2–3 weeks. To estimate a specific workout, use the calorie burn calculator.

Using TDEE for Weight Loss

For sustainable fat loss, create a moderate deficit of 300–500 calories below your TDEE. Using the common approximation of about 7,700 kcal per kg of body fat, that is roughly 0.3–0.5 kg per week at first, usually slowing over time as your body adapts. Moderate deficits are generally easier to sustain; very large deficits tend to increase hunger and the share of lean mass lost. Use our Calorie Calculator to get specific targets.

Using TDEE for Muscle Gain

Building muscle requires a calorie surplus — typically 200–500 calories above TDEE combined with progressive resistance training and adequate protein. A "lean bulk" with a small surplus (200–300 kcal) minimizes fat gain while supporting muscle growth. For optimal macronutrient distribution during a bulk, use our Macro Calculator and ensure protein intake is at least 1.6–2.2 g/kg body weight via our Protein Calculator.

Why You Shouldn't Eat Below BMR

While creating a calorie deficit is necessary for weight loss, eating well below your estimated BMR for long periods makes it harder to meet nutrient needs, increases lean-mass loss and is linked to fatigue and hormonal changes. Your BMR is itself an estimate, so treat it as a practical floor rather than a precise limit, and create deficits from your TDEE. Very-low-calorie diets should be medically supervised.

How TDEE Changes Over Time

Your TDEE is not a fixed number — it shifts as your body changes. Weight loss reduces BMR (smaller bodies burn fewer calories), prolonged dieting can lower expenditure somewhat more than weight loss alone predicts (adaptive thermogenesis), and changes in activity level directly affect your expenditure. Real-world TDEE can therefore differ from any formula; your weight trend over several weeks is the best check. Recalculate your TDEE every 4–6 weeks or after losing/gaining 5+ kg. If weight loss stalls despite consistent tracking, your TDEE may have decreased and needs recalibration.

Complete Privacy

All calculations are performed in your browser. Your personal information — age, weight, height, sex — is never sent to any server or stored. SnapBodyCalc is built with privacy as a core principle. Analytics and web fonts still make standard requests that include your IP address and the page URL — but never your measurements.