IIFYM Calculator (If It Fits Your Macros)

The calculator first estimates your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, which is widely considered the gold standard for clinical and fitness estimations. For males, BMR is calculated as 10 * weight(kg) + 6.25 * height(cm) - 5 * age + 5. For females, the constant becomes -161 instead of +5. This baseline is multiplied by your activity factor to find your Total Daily Energy Expenditure (TDEE). From there, macronutrients are distributed using standard energy densities: proteins and carbohydrates provide approximately 4 calories per gram, while dietary fats provide 9 calories per gram.

Consider a 30-year-old male who weighs 80 kg, stands 180 cm tall, and exercises moderately with an activity factor of 1.55. First, his BMR is calculated: (10 * 80) + (6.25 * 180) - (5 * 30) + 5 = 800 + 1125 - 150 + 5 = 1780 calories. Multiplying this by his activity factor of 1.55 yields a TDEE of approximately 2,759 calories. Depending on his primary fitness goal—such as muscle building or fat loss—his macronutrient split is then derived using percentage ranges, ensuring adequate protein intake for muscle recovery alongside balanced carbs and fats for sustained energy.

For the best results, use a digital food scale to weigh your food in grams rather than relying on volume measurements, which can be highly inaccurate. Remember that macro targets are dynamic; as your body weight changes, your TDEE will shift, requiring periodic recalculation every few weeks. Finally, prioritize consistency over perfection—getting within a few grams of your target daily macros is usually enough to drive steady progress.