How to Calculate Your TDEE and Macros (A No-Nonsense Guide to Nutrition Maths)

You've probably heard "calories in, calories out." It's a simplification — but it's not wrong. The foundation of any successful body composition change is understanding your TDEE (Total Daily Energy Expenditure) and setting macronutrient targets that support your goal. This guide explains the formulas, the science, and how to apply it in practice.

What Is TDEE?

TDEE is the total number of calories your body burns in a 24-hour period, accounting for everything: basic biological functions, digestion, movement, and exercise. It has four components:

• BMR (Basal Metabolic Rate) — calories burned at complete rest to sustain life (~60–70% of TDEE)
• TEF (Thermic Effect of Food) — energy used to digest and process food (~10% of TDEE)
• EAT (Exercise Activity Thermogenesis) — calories burned during intentional exercise (~15–30%)
• NEAT (Non-Exercise Activity Thermogenesis) — all movement outside exercise (fidgeting, walking, standing)

NEAT is the most variable component and explains why some people seem to "eat whatever they want" — they have high NEAT, often unconsciously moving more and burning hundreds of extra calories daily.

The BMR Formula: Mifflin-St Jeor

The most accurate formula for estimating BMR for the general population is the Mifflin-St Jeor equation, validated in multiple studies and recommended by the Academy of Nutrition and Dietetics.

Example Calculation

This is the number of calories he'd burn lying in bed doing absolutely nothing for 24 hours. To get TDEE, multiply by an activity factor.

Activity Multipliers

Using our example: 1,767.5 × 1.55 (moderately active) = 2,739 calories TDEE

Most people overestimate their activity level. "Moderately active" means deliberate structured exercise 3–5 days per week. If you go to the gym twice a week and sit at a desk the rest of the time, you're likely "lightly active."

Setting Calories for Your Goal

Losing Weight (Calorie Deficit)

To lose approximately 0.5kg per week, create a 500 calorie daily deficit (3,500 calories per week ≈ 0.5kg of fat). This is the standard evidence-based recommendation.

• Deficit target: TDEE − 500
• Aggressive (1kg/week): TDEE − 1,000 (not recommended long-term)
• Minimum: Never go below 1,200 calories (women) or 1,500 calories (men)

Gaining Muscle (Calorie Surplus)

Muscle gain is slower than fat loss — expect 0.5–1kg of actual muscle per month under ideal conditions. A modest surplus of 200–300 calories is sufficient to support muscle growth without excessive fat gain.

Maintenance

Eating at TDEE maintains your current weight. This is also the starting point for body recomposition — losing fat and gaining muscle simultaneously (possible for beginners and returning athletes, harder for advanced trainees).

Macronutrients: What They Are and Why They Matter

Calories tell you how much to eat. Macronutrients tell you what to eat. There are three:

• Protein: 4 calories per gram — essential for muscle repair, satiety, immune function
• Carbohydrates: 4 calories per gram — primary energy source, especially for exercise
• Fat: 9 calories per gram — hormonal health, brain function, fat-soluble vitamins

How to Set Your Macros

The order of operations matters:

Step 1: Set Protein

Protein is the most important macro for body composition. It preserves muscle during a deficit and supports growth during a surplus. The evidence-based target is:

Step 2: Set Fat

Fat is essential for hormone production (including testosterone). Going too low on fat has real health consequences. A minimum of 0.8–1g per kg bodyweight, or 20–30% of total calories, is recommended.

Step 3: Fill the Rest with Carbs

Carbohydrates are not essential in the same biochemical sense as protein and fat, but they fuel performance and are generally the most enjoyable macro to eat. Fill remaining calories with carbs.

How Accurate Are These Calculations?

TDEE formulas have a margin of error of approximately ±10%. This means your real maintenance calories could be 200–300 calories higher or lower than the formula predicts. Individual variation comes from:

• Genetic differences in metabolic efficiency
• Gut microbiome composition
• Hormonal status (thyroid, insulin, cortisol)
• Amount of lean muscle mass
• History of dieting (adaptive thermogenesis)

The formula is a starting point, not a verdict. Use it as a baseline and adjust based on real-world results over 2–3 weeks. If you're not losing weight on your calculated deficit, reduce calories by 100–150 and reassess.

Common Mistakes When Tracking Calories

1. Underestimating Portions

Studies consistently show people underestimate calories by 30–50%. A "tablespoon" of peanut butter poured generously is often 1.5–2 tablespoons. Weigh food on a scale rather than using volume measures for accuracy.

2. Forgetting Liquid Calories

Coffee with milk, juice, alcohol, protein shakes, and cooking oils add up quickly. A 250mL glass of orange juice is ~110 calories with no satiety benefit. Track everything.

3. Not Eating Enough Protein

Most people eating a standard diet get 70–100g of protein. At 80kg bodyweight, this is 40–60% below the target for body recomposition. Prioritise protein at every meal.

4. Changing Too Many Variables at Once

Don't change calories, macros, and training simultaneously. Make one change, run it for 2–3 weeks, assess results, then adjust. You can't identify what's working if everything changes at once.

Do I Need to Track Macros Forever?

No. Tracking is a tool for building awareness, not a lifelong obligation. Most people who track for 3–6 months develop an accurate intuitive understanding of their food intake. After that, periodic check-ins during cutting or bulking phases are usually sufficient.

TDEE and Macros for Different Goals

The Relationship Between TDEE and Exercise

Exercise increases TDEE through EAT (calories burned during exercise). But there's a crucial insight from recent research: total daily energy expenditure doesn't scale linearly with exercise.

Studies by Herman Pontzer and colleagues found that beyond moderate activity levels, the body compensates by reducing NEAT and metabolic activity in other areas. This "constrained total energy expenditure" model explains why intensive exercise alone is ineffective for weight loss — diet is the primary lever.

This doesn't mean exercise is unimportant — it's essential for health, muscle retention, and cardiovascular fitness. But it means you can't "out-exercise" a poor diet, and your calculated TDEE should be used with diet as the primary variable.

Frequently Asked Questions

Should I eat back exercise calories?

If you used the TDEE method with an activity multiplier, your exercise calories are already included in your target — don't add them back. If you used sedentary TDEE plus a separate exercise estimate, then yes, add back a portion (typically 50–75% to account for overestimation).

How do I know if my activity multiplier is right?

If you're eating at your calculated maintenance and not maintaining weight over 2–3 weeks, your multiplier is wrong. Adjust by 100–150 calories and reassess. Real-world calibration beats formula precision.

What about keto, low-carb, or other diets?

Total calories remain the primary driver of body composition. Low-carb diets reduce carbs and increase fat ratios. Keto minimises carbs to achieve ketosis. Both can be effective if they help you maintain a calorie deficit. The macro calculator can be adjusted — just increase fat and reduce carbs proportionally.

How does body fat affect TDEE?

Lean mass (muscle) is metabolically active and increases BMR. Fat tissue burns minimal calories. Two people at the same weight can have significantly different TDEEs if one is leaner. Use our Body Fat Calculator to estimate your lean mass.