How to Calculate Your Macros for Muscle Building or Fat Loss

Calculating macros is not guesswork — it is applied arithmetic layered on top of established physiology. The process has four steps: estimate your total daily energy expenditure (TDEE), set protein, set fat, and assign carbohydrates to the remainder. Each step has a defensible scientific basis.

Step 1: Calculate TDEE

Your Total Daily Energy Expenditure is the number of calories your body burns across all activity. The most widely validated resting metabolic rate equation is the Mifflin-St Jeor formula:

Men: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Multiply your RMR by an activity multiplier:

This gives you maintenance calories. Use the macro calculator to run these numbers automatically.

Important caveat: TDEE equations are population averages with ±10–15% individual error. Track your weight for 2 weeks at maintenance calories. If you gain, reduce by 100–150 kcal. If you lose, add 100–150 kcal. Real-world data always beats formula estimates.

Step 2: Set Protein First

Protein is the most critical macro for body composition. The current evidence from meta-analyses, including Morton et al. (2018), shows that muscle protein synthesis is maximised at approximately 1.6 g/kg/day, with a ceiling closer to 2.2 g/kg/day for leaner, harder-training individuals.

A practical target: 2 g/kg of body weight (or 0.9 g/lb). This slightly exceeds the minimum effective dose, providing a buffer for variation in absorption, meal distribution, and training intensity.

For a 80 kg person: 80 × 2 = 160 g protein/day = 640 kcal from protein (protein provides 4 kcal/g)

During a caloric deficit, evidence from Helms et al. (2014) suggests protein needs increase to 2.3–3.1 g/kg of lean body mass in resistance-trained athletes, because amino acids compete with gluconeogenesis. If you are cutting, lean toward the higher end of the range.

For more depth on protein timing and distribution, see how much protein to build muscle.

Step 3: Set a Fat Floor

Dietary fat is essential for hormone production, fat-soluble vitamin absorption (A, D, E, K), and cell membrane integrity. Dropping fat too low — a common mistake on aggressive cuts — suppresses testosterone and disrupts recovery.

The evidence-supported minimum is 0.8 g/kg/day. For body composition goals, a practical target is 1 g/kg/day, which provides adequate substrate without consuming too many calories.

For a 80 kg person: 80 × 1 = 80 g fat/day = 720 kcal from fat (fat provides 9 kcal/g)

Do not drop fat below the minimum floor even in aggressive cuts. If calories need to drop further, reduce carbohydrates.

Step 4: Fill Remaining Calories with Carbohydrates

Once protein and fat are set, carbohydrates fill the remainder:

Carbs (g) = (TDEE − protein kcal − fat kcal) ÷ 4

For the 80 kg person at TDEE 2,800 kcal (maintenance):

• Protein: 160 g = 640 kcal
• Fat: 80 g = 720 kcal
• Remaining: 2,800 − 640 − 720 = 1,440 kcal ÷ 4 = 360 g carbohydrate

Carbohydrates are the primary fuel for anaerobic exercise. Higher carbohydrate availability directly supports training performance, which in turn drives the adaptations that build muscle. Do not artificially restrict carbs unless you have a specific medical reason to do so.

Cutting Adjustments

A deficit of 300–500 kcal below TDEE is the most evidence-supported range for fat loss while preserving muscle (discussed in detail in a separate post on calorie deficits). Apply the deficit by reducing the carbohydrate allocation — protein and fat floors stay constant.

Example cut (−400 kcal from maintenance):

• New calorie target: 2,800 − 400 = 2,400 kcal
• Protein: 160 g (640 kcal) — unchanged
• Fat: 80 g (720 kcal) — unchanged
• Carbs: (2,400 − 640 − 720) ÷ 4 = 260 g (down from 360 g)

Bulking Adjustments

A surplus of 200–400 kcal above TDEE supports muscle gain without excessive fat accumulation. The upper limit of muscle gain for natural lifters is approximately 0.5–1 kg per month, meaning a large surplus simply adds fat rather than extra muscle.

Apply the surplus to carbohydrates. If digestion is a problem at very high carb intakes, add a small amount of fat instead.

Common mistakes:

• Setting protein too low: many people under-eat protein while over-eating carbs or fat
• Ignoring the fat floor: fat below 0.8 g/kg impairs hormones, especially testosterone
• Not recalculating as weight changes: as you lose or gain weight, your TDEE shifts — recalculate every 4–6 weeks
• Treating macros as exact: hitting ±5 g on each macro is sufficient — do not obsess over single-gram precision
• Forgetting dietary fibre: aim for 25–40 g of fibre per day within your carbohydrate allocation

Summary

Use the macro calculator to handle the arithmetic automatically and get personalised targets for your current weight, height, and activity level.

GYMRPG’s nutrition log tracks daily macro and calorie intake alongside the workout log, storing both in the same app.