Macro Calculator

What are macros?

Macronutrients — or macros — are the three main energy-providing nutrients in food: protein, carbohydrates, and fat. Each supplies a specific number of calories per gram: protein and carbs each deliver 4 kcal/g, while fat delivers 9 kcal/g. Hitting your daily calorie target is the single biggest lever for changing body weight; how you split those calories between protein, carbs, and fat determines your body composition — how much of any weight change is muscle versus fat.

What is IIFYM (If It Fits Your Macros)?

IIFYM stands for If It Fits Your Macros. Rather than following a rigid meal plan with specific "allowed" foods, IIFYM gives you a daily target for each macronutrient and lets you choose any foods that add up to those numbers. The approach blends the precision of counting with the flexibility to include any food you enjoy, which makes it easier to stick to long-term than restrictive diets.

The flexibility does not mean anything goes — you still need to hit your calorie target and ideally prioritise micronutrient-dense whole foods. But within those constraints, a Friday-night takeaway that fits your macros is perfectly compatible with your goals.

How the macro split is calculated

This calculator first computes your TDEE (Total Daily Energy Expenditure) using the Mifflin-St Jeor equation — or the Katch-McArdle formula if you supply a body-fat percentage — then multiplies it by a two-axis activity factor (daily occupation + structured exercise). See the TDEE calculator for a deeper breakdown of that step.

Your selected goal then applies a calorie adjustment to the TDEE to produce your daily target (with a 1,200 kcal floor for safety):

• Lose weight — −500 kcal deficit (≈ 0.5 kg / 1 lb per week)
• Maintain — no adjustment
• Gain muscle — +300 kcal surplus (lean bulk, minimises fat gain)

That calorie total is then divided between protein, carbs, and fat according to the chosen diet preset:

• Balanced — 30% protein / 40% carbs / 30% fat — the evidence-backed starting point for most people
• High-Protein — 40% / 30% / 30% — ideal when building or preserving muscle, or on a deficit
• Low-Carb — 40% / 20% / 40% — reduces carbohydrate and raises fat; suits those sensitive to carbs
• High-Carb — 25% / 55% / 20% — maximises glycogen for endurance athletes and heavy training days

Grams are calculated by dividing the allocated calories by the caloric density of each nutrient: (target kcal × ratio) ÷ 4 for protein or carbs, ÷ 9 for fat.

Which diet preset should I choose?

Balanced is the right default for most people. High-Protein is the best choice when you are on a calorie deficit and want to preserve muscle — protein is satiating and muscle-sparing. Low-Carb suits anyone who finds carbs trigger cravings or blood-sugar spikes. High-Carb is designed for endurance athletes or people doing heavy daily training who need full glycogen stores. You can also use the calorie deficit calculator to model the deficit side independently, or the protein intake calculator to fine-tune your protein target.

Turning your macros into real meals

Swoodie auto-calculates your macro targets from your profile and then tracks every meal against them in real time. Scan a plate or barcode and the app logs the protein, carbs, and fat instantly — no manual entry needed. It can also generate recipes and a weekly meal plan that hit your remaining macro budget for the day. If your primary aim is fat loss, see the full weight-loss guide.

This tool provides general estimates for healthy adults and is not medical advice. For personalised dietary guidance or if you have a medical condition, consult a registered dietitian or doctor.

Frequently asked questions