Macro Calculator (IIFYM — If It Fits Your Macros)

Calculate your TDEE and daily macro targets for weight loss, maintenance or muscle gain.

How the Macro Calculator Works

This calculator uses the Mifflin-St Jeor equation — the most accurate BMR formula for the general population — to estimate your Basal Metabolic Rate. BMR is then multiplied by an activity factor to give your Total Daily Energy Expenditure (TDEE). A goal adjustment is applied: −500 kcal for weight loss (approximately 1 lb/week), 0 for maintenance, or +300 kcal for lean muscle gain. Macros are then split by goal: Lose Weight uses 40% protein / 30% carbs / 30% fat to preserve muscle during a deficit; Maintain uses 30/40/30; Gain Muscle uses 35% protein / 45% carbs / 20% fat to fuel performance. Protein and carbs yield 4 kcal/g; fat yields 9 kcal/g. Fibre targets follow the Dietary Reference Intake: 38 g/day for men, 25 g/day for women. IIFYM (If It Fits Your Macros) means that as long as you hit these daily targets, your food choices are flexible.

Frequently Asked Questions

What is IIFYM (If It Fits Your Macros)?
IIFYM is a flexible dieting approach that tracks macronutrients (protein, carbs, fat) rather than specific foods. As long as you hit your daily macro targets, food choices are flexible.
How do I calculate my TDEE?
TDEE (Total Daily Energy Expenditure) = BMR × activity factor. BMR is calculated with the Mifflin-St Jeor equation: for men, BMR = 10×kg + 6.25×cm − 5×age + 5.
How much protein do I need per day?
Most research supports 0.7–1g of protein per lb of bodyweight for active individuals. This calculator sets protein at 30–40% of calories depending on your goal.
Should I eat at a deficit or surplus to build muscle?
A modest surplus of 200–500 calories is optimal for muscle gain while minimising fat storage. Aggressive bulking (1,000+ calorie surplus) adds mostly fat.

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