Iron Intake Calculator

A macronutrient (macro) calculator determines how many grams of protein, carbohydrate, and fat you should consume daily to hit your calorie target while supporting your fitness or health goal. While total calorie balance determines whether weight is gained or lost, the macronutrient ratio within that calorie budget influences body composition, energy levels, training performance, satiety, and long-term metabolic health. For anyone going beyond basic calorie counting — especially athletes, bodybuilders, people managing specific health conditions, or those on structured diets — macro tracking provides the next level of precision. and are related tools for building a complete nutrition framework.

Different dietary frameworks emphasise different macro splits: ketogenic diets use very low carbohydrate (5–10% of calories) and high fat (70–75%); traditional bodybuilding approaches use moderate fat, high carbohydrate, and very high protein; Zone diet targets 40% carb/30% protein/30% fat; endurance sport nutrition typically emphasises carbohydrate at 55–65% of total intake. The "best" split depends entirely on individual response, goal, and preference.

1. Enter your daily calorie target (use your TDEE calculator result adjusted for your goal).
2. Set your protein target first — protein is the most important macro to get right. Enter grams per kg of body weight (1.6g/kg for maintenance; 2.0–2.4g/kg during a fat loss deficit or muscle-building phase).
3. Set your fat target — a minimum of 0.8g/kg body weight is needed for hormone production and fat-soluble vitamin absorption; typical ranges are 25–35% of total calories.
4. Carbohydrates fill the remaining calories: remaining kcal ÷ 4 = carbs in grams (carbs provide 4 kcal/g).
5. Read the daily macro targets in grams and as percentages of total calories.
6. Use a food tracking app (Cronometer, Chronometer, or MyFitnessPal) to hit these targets consistently — the first week reveals which foods naturally support each macro.

Macronutrient calculation formulas

Protein kcal = Protein g × 4. Carbohydrate kcal = Carb g × 4. Fat kcal = Fat g × 9.

Carbs g = (Total kcal − Protein kcal − Fat kcal) ÷ 4

Worked example: 2,200 kcal target, 80 kg male. Protein: 80 kg × 2.0g = 160g protein = 640 kcal. Fat: 80 kg × 1.0g = 80g fat = 720 kcal. Remaining for carbs: 2,200 − 640 − 720 = 840 kcal ÷ 4 = 210g carbohydrate. Split: 29% protein / 38% carb / 33% fat — a balanced macro profile suited to body recomposition.

Understanding your macro split

Common macro ratio profiles

Standard balanced (maintenance): 25–30% protein / 40–50% carbs / 25–30% fat. Fat loss (moderate carb): 35% protein / 35% carbs / 30% fat. Ketogenic: 20–25% protein / 5–10% carbs / 65–75% fat. Endurance sport: 20% protein / 55–65% carbs / 20–25% fat. Muscle gain: 30% protein / 45% carbs / 25% fat. Note: percentage targets are less precise than gram targets because calories change while percentages shift. Prioritise hitting protein in grams, then fat in grams, and let carbs fill the remainder.

Health tips and best practices

• Protein is the macro to prioritise above all others — at 2.0g/kg of body weight during a deficit, it preserves muscle, increases satiety, and has the highest thermic effect (30% of calories consumed are burned in digestion).
• Don't fear dietary fat — dietary fat does not directly translate to body fat; it is essential for testosterone production, vitamin absorption (A, D, E, K), and cell membrane integrity. Minimum 0.8g/kg/day.
• Carbohydrate timing matters for athletes: consume the majority of daily carbs in the meals before and after training to fuel performance and recovery glycogen replenishment.
• Fibre is a component of carbohydrate (and contributes fewer net calories): aim for 25–35g/day for satiety and gut health — a high-carb diet with poor fibre content produces hunger and digestive issues.
• Track macros for 4–8 weeks to learn the macro profile of your usual food choices — once internationalised, most people can maintain targets without precise daily tracking.
• Alcohol contains 7 kcal/g and competes with fat oxidation metabolically — even within a calorie target, regular alcohol disrupts fat loss progress.

• Protein requirement for muscle retention during calorie restriction: 1.6–2.4g/kg/day — the higher end of the range is more protective during aggressive deficits (Morton et al., BJSM, 2018).
• Dietary fat minimum for hormonal health: 0.8–1.0g/kg/day — below this, testosterone levels in males decline measurably within weeks (Hamalainen et al., 1984).
• Carbohydrate provides 4 kcal/g; fat 9 kcal/g — this 2.25× calorie density difference means small amounts of fat-rich foods (nuts, cheese, oils) significantly affect total calorie intake.
• A keto adaptation period of 3–6 weeks is typically required before fat becomes the primary fuel source — performance typically drops during the transition phase before recovering.

Common mistakes to avoid

• Tracking macros by percentage only rather than absolute grams — if total calorie intake shifts, percentage targets produce different gram amounts, making it harder to hit protein targets consistently.
• Cutting dietary fat too aggressively in a fat loss phase — below 0.8g/kg/day, hormonal disruption, poor vitamin absorption, and inadequate essential fatty acid intake become significant risks.
• Relying on restaurant or meal delivery nutrition data without accounting for portion variation — restaurant calorie counts are often inaccurate by ±20–40%.
• Ignoring fibre as a component of carbohydrate — a plan hitting carb gram targets with poor food quality (refined carbs, no vegetables) produces hunger, poor gut health, and reduced micronutrient intake.

Macronutrient targets calculated by this tool are based on generalised formulas and published nutritional research. Individual needs vary based on health status, medications, metabolic conditions, training volume, and dietary preferences. This calculator does not constitute medical or nutritional advice. For medical conditions affecting macronutrient requirements (diabetes, kidney disease, phenylketonuria, eating disorders), consult a registered dietitian (RD) before modifying your diet. UK dietary reference values are published by the Scientific Advisory Committee on Nutrition (SACN) at gov.uk.