The IIFYM (If It Fits Your Macros) Calculator helps you determine your daily macronutrient targets — protein, carbohydrates, and fats — based on your body composition, activity level, and fitness goals. Whether you’re aiming for weight loss, muscle gain, or maintenance, this tool provides personalized calorie and macro recommendations to guide your nutrition planning.
Designed for fitness enthusiasts, athletes, and anyone tracking their diet, the IIFYM approach offers flexibility while ensuring you meet your nutrient needs. Simply enter your age, gender, weight, height, activity level, and goal, and the calculator will estimate your Total Daily Energy Expenditure (TDEE) and break it down into grams of protein, carbs, and fat. Use the results to build meal plans that fit your lifestyle without rigid restrictions.
⚙️ Your Macros
How to Use This Tool
Enter your age, gender, weight, height, activity level, and goal. The calculator uses the Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR), then multiplies by an activity factor to get Total Daily Energy Expenditure (TDEE). Based on your goal (lose, maintain, or gain), it adjusts calories and sets protein at 2.0 g per kg of body weight, fat at 0.8 g per kg, and fills the remaining calories with carbohydrates.
💡 Tip: For best results, use your current weight and be honest about your activity level. Recalculate every 4-6 weeks as your weight changes.
Formula Explained
The Mifflin-St Jeor equation is widely regarded as one of the most accurate BMR formulas:
- Male BMR: 10 × weight (kg) + 6.25 × height (cm) – 5 × age (years) + 5
- Female BMR: 10 × weight (kg) + 6.25 × height (cm) – 5 × age (years) – 161
TDEE = BMR × Activity Factor. Activity factors range from 1.2 (sedentary) to 1.9 (very active). The calorie adjustment for goals: lose weight = –20%, slow loss = –10%, maintain = 0%, slow gain = +10%, gain weight = +20%.
Worked Examples
Example 1: 30-year-old male, 80 kg, 180 cm, moderate activity (1.55), maintain goal.
BMR = 10×80 + 6.25×180 – 5×30 + 5 = 800 + 1125 – 150 + 5 = 1780 kcal.
TDEE = 1780 × 1.55 = 2759 kcal.
Target calories = 2759 kcal. Protein = 80×2.0 = 160 g (640 kcal). Fat = 80×0.8 = 64 g (576 kcal). Carbs = (2759 – 640 – 576) / 4 = 385.75 g.
Example 2: 25-year-old female, 65 kg, 165 cm, light activity (1.375), lose weight goal.
BMR = 10×65 + 6.25×165 – 5×25 – 161 = 650 + 1031.25 – 125 – 161 = 1395.25 kcal.
TDEE = 1395.25 × 1.375 = 1918.47 kcal.
Target calories = 1918.47 × 0.8 = 1534.78 kcal. Protein = 65×2.0 = 130 g (520 kcal). Fat = 65×0.8 = 52 g (468 kcal). Carbs = (1534.78 – 520 – 468) / 4 = 136.7 g.
Tips & Best Practices
- Use a food scale and tracking app (like MyFitnessPal or Cronometer) to log your intake accurately.
- Prioritize whole foods — fruits, vegetables, lean proteins, healthy fats — even if they fit your macros.
- Adjust protein upward (2.2–2.5 g/kg) if you're in a calorie deficit to preserve muscle mass.
- Reassess your TDEE every 5-10 lbs of weight change.
Frequently Asked Questions
Is IIFYM the same as flexible dieting? Yes, IIFYM is often called flexible dieting because it allows any foods as long as they fit your daily macro targets.
Do I need to track micronutrients? While IIFYM focuses on macros, it's still important to eat a variety of nutrient-dense foods to meet vitamin and mineral needs. Consider using a USDA FoodData Central database to check micronutrient content.
Can I use this calculator for bulking? Yes, select "Gain Weight" or "Slow Gain" to add a calorie surplus. Adjust protein and fat as needed for muscle growth.
What if my carb calculation is negative? This can happen if protein and fat calories exceed your target. Increase your calorie target or reduce fat/protein slightly.
Additional Resources
For more detailed information on macronutrient recommendations, visit the American College of Sports Medicine or the USDA Nutrition Evidence Library. For a deeper dive into the Mifflin-St Jeor equation, see the original study: Mifflin MD, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990;51(2):241-247.