How to Calculate Your Macros for Fat Loss: The Complete Guide

What Are Macros and Why Do They Matter?

Macronutrients are the three main categories of nutrients your body needs in large quantities: protein, carbohydrates, and fat. While calories tell you how much energy you're consuming, macros tell you where that energy is coming from — and that distinction is what separates someone who loses weight from someone who loses fat while preserving muscle.

Step 1: Calculate Your Basal Metabolic Rate (BMR) with the Mifflin-St Jeor Equation

The Mifflin-St Jeor equation is considered the gold standard for estimating caloric needs. Published in 1990, it remains the most accurate predictive formula for resting metabolic rate. Here's how it works:

• check_circleFor men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
• check_circleFor women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161
• check_circleExample: A 28-year-old male, 80 kg, 175 cm → BMR = (10 × 80) + (6.25 × 175) - (5 × 28) + 5 = 800 + 1093.75 - 140 + 5 = 1,758 calories

Step 2: Apply Your Activity Multiplier (TDEE)

Your BMR is only what your body burns at rest. To find your Total Daily Energy Expenditure (TDEE), multiply your BMR by your activity level:

• check_circleSedentary (desk job, little exercise): BMR × 1.2
• check_circleLightly active (exercise 1–3 days/week): BMR × 1.375
• check_circleModerately active (exercise 3–5 days/week): BMR × 1.55
• check_circleVery active (hard exercise 6–7 days/week): BMR × 1.725
• check_circleExtremely active (athlete or physical job + training): BMR × 1.9

Step 3: Set Your Caloric Target Based on Your Goal

Now that you know your TDEE, adjust it based on your goal. For fat loss, a moderate deficit of 300–500 calories below TDEE is sustainable and effective. For muscle gain, add 200–300 calories above TDEE. For maintenance, eat at your TDEE.

• check_circleFat loss: TDEE - 400 calories (moderate, sustainable deficit)
• check_circleMuscle gain: TDEE + 250 calories (lean bulk, minimise fat gain)
• check_circleMaintenance: Eat at TDEE

Step 4: Split Your Calories Into Macros

This is where the magic happens. A common evidence-based split for fat loss with muscle preservation is:

• check_circleProtein: 1.6–2.2g per kg of body weight (prioritise this first — it's the most important macro for body composition)
• check_circleFat: 0.7–1.0g per kg of body weight (essential for hormonal health)
• check_circleCarbohydrates: Fill the remaining calories with carbs (your primary fuel source for training)
• check_circleRemember: Protein = 4 cal/g, Carbs = 4 cal/g, Fat = 9 cal/g

A Real-World Example

Let's put it all together. Sarah is a 30-year-old woman, 65 kg, 163 cm, moderately active, with a goal of fat loss. Her BMR = (10 × 65) + (6.25 × 163) - (5 × 30) - 161 = 1,357 calories. Her TDEE = 1,357 × 1.55 = 2,103 calories. For fat loss: 2,103 - 400 = 1,703 calories. Her macros: Protein = 130g (520 cal), Fat = 55g (495 cal), Carbs = 172g (688 cal). Total = 1,703 calories.

Common Mistakes to Avoid

Many people overcomplicate macro tracking or make errors that stall progress. Here are the most common pitfalls:

• check_circleSetting protein too low — aim for at least 1.6g/kg even when cutting
• check_circleCutting fat too aggressively — your hormones will suffer below 0.5g/kg
• check_circleObsessing over exact numbers — a ±50 calorie variance day-to-day is totally fine
• check_circleIgnoring fibre — aim for 25–35g daily for gut health and satiety
• check_circleNot adjusting over time — recalculate every 4–6 weeks as your weight changes

Skip the Spreadsheet — Let MealGrid Do the Maths

Understanding the science is powerful, but you don't have to do these calculations manually every day. MealGrid's built-in calculator uses the Mifflin-St Jeor equation to set your targets, then generates personalised recipes that hit those exact macros — so you can focus on cooking, eating, and living instead of crunching numbers.