What are macronutrients?
Macronutrients — protein, carbohydrates, and fat — are the three nutrients that provide calories. Every calorie you eat comes from one of these three sources. Protein and carbohydrates each supply 4 kcal per gram; fat supplies 9 kcal per gram. Alcohol provides 7 kcal/g but is not a macronutrient because it serves no structural function.
While total calorie balance determines whether you gain or lose weight, your macro split determines what you gain or lose — muscle, fat, or both. This is why two people eating the same calories can have dramatically different body composition outcomes depending on how those calories are distributed.
The protein-first approach
Protein is the structural priority in any nutrition plan. It is the only macronutrient that directly supports muscle protein synthesis (building) and protects existing muscle during a caloric deficit. Unlike carbs and fat, there is no protein storage depot in the body — dietary protein must be supplied regularly.
The evidence base for protein targets is robust:
- •Muscle maintenance: 1.2–1.6 g/kg body weight is sufficient for sedentary to moderately active individuals to maintain lean mass.
- •Fat loss (cut): 2.0–2.4 g/kg is recommended during a deficit to minimise muscle loss. Muscle is metabolically expensive tissue that the body is willing to break down for energy when calories are restricted.
- •Muscle building (bulk): 1.6–2.2 g/kg supports maximal muscle protein synthesis. Beyond 2.2 g/kg, additional benefit is marginal for most people.
This calculator uses 2.2 g/kg for a cut, 1.8 g/kg for maintenance, and 2.0 g/kg for a bulk — all within the evidence-supported range.
The fat floor — why you need dietary fat
Dietary fat has been demonised for decades, but it is essential. Fat is required for:
- •Hormone production: Sex hormones (testosterone, estrogen, progesterone) and steroid hormones are synthesised from cholesterol. Very low fat intakes suppress hormone levels.
- •Fat-soluble vitamins: Vitamins A, D, E, and K require dietary fat for absorption. Without adequate fat, deficiencies develop even if you eat vitamin-rich foods.
- •Cell membranes: Every cell in your body has a lipid bilayer membrane. Dietary fat quality affects membrane fluidity and cell signalling.
- •Essential fatty acids: Omega-3 and omega-6 fatty acids cannot be synthesised by the body and must come from food.
Most sports nutrition guidelines set a fat floor of 20–25% of total calories, or approximately 0.8–1.0 g/kg body weight. This calculator uses 25% of target calories for fat — a safe, well-tolerated level that supports hormonal health without sacrificing too many calories that could go to protein and carbs.
Carbohydrate flexibility
After protein and fat targets are set, carbohydrates fill the remaining calories. This is sometimes called the “protein-first, fat-floor, carbs-fill” approach.
Carbohydrates are the primary fuel for high-intensity exercise. For athletes training at high volumes, higher carbohydrate intakes improve performance and recovery. For sedentary or lightly active individuals, carbs can be lower without meaningful performance consequences. The flexibility of carbs is what allows this framework to work across a wide range of dietary preferences — from higher-carb approaches to lower-carb diets.
There is no evidence that carbohydrates cause fat gain independently of total calorie balance. All three macros contribute to fat storage when consumed in excess of needs.
How to use your macro targets
Macro tracking is most effective when approached with proportionality:
- 1.Prioritise protein. Hit your protein target first. This is non-negotiable — consistent protein intake protects muscle regardless of whether you are cutting or bulking.
- 2.Don't slash fat too low. Respect the fat floor. Going below 20% for extended periods has hormonal consequences, particularly for women.
- 3.Flex carbs to preference. Adjust carbs up or down based on training demands, satiety, and how you feel. Athletes need more; lower-activity periods need less.
- 4.Recalculate every 4–6 weeks. As your weight changes, your TDEE and macro targets change too. Update your inputs regularly.
- 5.Track trends, not single days. Day-to-day variation is normal. What matters is the weekly average, not hitting targets precisely every day.
Frequently asked questions
What are macros?▾
Macros (macronutrients) are the three main energy-providing nutrients: protein, carbohydrates, and fat. Protein and carbs each provide 4 kcal per gram; fat provides 9 kcal per gram. Your macro split determines how your daily calories are distributed.
How much protein do I need to build muscle?▾
Research consistently supports 1.6–2.2 g of protein per kg of bodyweight for muscle growth. This calculator defaults to 2.0 g/kg for a muscle-gain goal. Higher intakes (up to 3.1 g/kg) may offer marginal benefit for advanced athletes or during a steep deficit.
Why is fat set at 25%?▾
Fat is essential for hormone production (especially testosterone and estrogen), fat-soluble vitamin absorption (A, D, E, K), and cell membrane integrity. Going below roughly 20% of calories from fat for extended periods can suppress hormones and impair health. 25% is a safe, well-tolerated floor.
How many calories should I cut to lose fat?▾
A deficit of 500 kcal/day produces roughly 0.5 kg (1 lb) of weight loss per week, which is considered a moderate, sustainable rate. This calculator applies a 500 kcal deficit for a cut goal. Deficits larger than 1,000 kcal/day risk muscle loss and metabolic adaptation.
What is a lean bulk?▾
A lean bulk uses a small caloric surplus (typically 200–400 kcal above TDEE) to maximize muscle gain while minimising fat accumulation. This calculator uses a +300 kcal surplus. Larger surpluses add fat faster without proportionally more muscle.
Should I hit macros or just calories?▾
Both matter. Hitting your protein target is the most important priority — protein protects muscle during a cut and enables growth during a bulk. Carbs and fat are more flexible based on preference and performance needs.