What are macros?
Macros — short for macronutrients — are the three main categories of nutrients that provide your body with energy: protein, carbohydrates and fat. Every food you eat is made up of some combination of these three, and each plays a distinct role in how your body functions, performs and changes over time.
Unlike micronutrients (vitamins and minerals), which you need in small amounts, macronutrients are needed in large quantities because they are your primary fuel source. Tracking macros — often called IIFYM (If It Fits Your Macros) — means focusing on hitting specific gram targets for each macronutrient, not just a total calorie number.
Protein
4 kcal per gram
Builds and repairs muscle tissue, supports immune function, keeps you full between meals. The most important macro for body composition.
Sources: Steak, Chicken, fish, eggs, Greek yoghurt, cottage cheese, tofu, legumes, whey protein
Carbohydrates
4 kcal per gram
Your body's preferred energy source. Fuels the brain, powers high-intensity exercise, and spares muscle protein from being broken down for energy.
Sources: Rice, oats, bread, pasta, potatoes, fruit, vegetables, beans
Fat
9 kcal per gram
Essential for hormone production, vitamin absorption (A, D, E, K), brain health and joint lubrication. The most calorie-dense macro.
Sources: Olive oil, avocado, nuts, seeds, oily fish, eggs, full-fat dairy
How it's calculated
1. BMR via Mifflin–St Jeor → 2. TDEE = BMR × activity multiplier → 3. Calorie target = TDEE ± goal adjustment → 4. Macros split: Protein 30–40% · Carbs 30–40% · Fat 25–35%
How your macro targets are calculated
This calculator uses the Mifflin–St Jeor equation to determine your Basal Metabolic Rate (BMR), then multiplies it by your activity level to get your Total Daily Energy Expenditure (TDEE). Your goal is then applied as a calorie adjustment. Finally, those calories are split into macros using evidence-based ratios optimised for your specific goal.
The ratios change depending on your goal. A weight loss plan prioritises higher protein to preserve muscle while in a deficit. A muscle gain plan increases carbs to fuel training and protein to support growth. Here are the macro splits used:
| Goal | Tag | Protein | Carbs | Fat | Calorie adj. |
|---|---|---|---|---|---|
| Aggressive cut | −500 kcal | 35% | 35% | 30% | −500 kcal/day |
| Cut | −250 kcal | 35% | 35% | 30% | −250 kcal/day |
| Maintain | ±0 kcal | 30% | 40% | 30% | ±0 kcal/day |
| Lean bulk | +250 kcal | 30% | 45% | 25% | +250 kcal/day |
| Aggressive bulk | +500 kcal | 30% | 45% | 25% | +500 kcal/day |
Macros for weight loss
When cutting, the single most important macro is protein. Research consistently shows that eating 1.6–2.4 g of protein per kg of bodyweight while in a calorie deficit is the most effective strategy for preserving lean muscle mass during fat loss. Lose the fat, keep the muscle — that is the goal.
Carbohydrates and fat can be adjusted according to preference. Many people find lower-carb approaches reduce hunger and make dieting easier; others perform better with moderate carbs, especially if they train regularly. Neither is universally superior — the best approach is the one you can sustain consistently.
Key principle
The biggest driver of weight loss is the calorie deficit, not the specific macro split. Get the deficit right first. Then optimise protein. Carbs and fat are flexible.
Macros for maintenance
Maintenance macros are what you eat to hold your current weight exactly where it is. This is more useful than it sounds: it is the foundation for understanding how your body responds to food, for diet breaks during longer cutting phases, and for body recomposition — the slow process of simultaneously losing fat and gaining muscle.
At maintenance, a balanced split of roughly 30% protein, 40% carbs and 30% fat works well for most active adults. If you find yourself gaining or losing weight consistently at your calculated maintenance, adjust total calories by 100 kcal and reassess after two weeks.
Macros for muscle gain (bulking)
Building muscle requires two things above all else: a calorie surplus and adequate protein. The surplus provides the raw energy needed for muscle protein synthesis; the protein provides the amino acid building blocks. Carbohydrates play a supporting role by fuelling training sessions and replenishing muscle glycogen post-workout.
A lean bulk — a modest surplus of 200–300 kcal — minimises fat gain while still providing enough energy for muscle growth. This approach is slower than an aggressive bulk but produces a much better muscle-to-fat ratio over time. Patience here pays dividends.
Training requirement
A calorie surplus alone does not build muscle. Without progressive resistance training, extra calories simply become fat. Make sure your training programme provides a sufficient stimulus for growth.
Why protein is the most important macro
Regardless of your goal, protein is the macro that most directly determines your body composition outcome. It is the only macro that builds and preserves muscle tissue. Here are the evidence-based protein targets for each goal:
| Goal | Protein target |
|---|---|
| Minimum (sedentary adult) | 0.8 g/kg |
| Weight loss (muscle retention) | 1.6–2.4 g/kg |
| Maintenance (active adult) | 1.4–2.0 g/kg |
| Muscle gain | 1.6–2.2 g/kg |
| Maximum studied benefit | 2.2–3.1 g/kg |
Higher protein intakes (above 3 g/kg) have not been shown to cause harm in healthy adults and may help satiety during aggressive cuts. The cost is simply less room for carbs and fat in your daily calorie budget.
Limitations of macro calculators
Macro targets are starting points, not precise prescriptions. Several factors mean your real-world response will vary:
- •Individual metabolism: TDEE formulas are population averages. Your real maintenance calories may be 10–20% higher or lower. Calibrate against real-world weight changes over 2–3 weeks.
- •Food label inaccuracy: Nutrition labels are allowed to be off by up to 20%. Restaurant meals are even less predictable. Precision tracking has diminishing returns — consistency matters more.
- •Training type and volume: High-volume endurance athletes need far more carbs than the ratios here suggest. Powerlifters may need less. Adjust based on performance and recovery.
- •Hormones and sleep: Poor sleep and high cortisol (stress) significantly impair fat loss and muscle gain regardless of how perfect your macros are.
Remember
Macro tracking is a tool, not a religion. It is highly effective for reaching body composition goals, but obsessive tracking can be counterproductive and may not suit everyone. A simpler approach — eating mostly whole foods with adequate protein — achieves similar results for many people.
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