What is a Macro Calculator?
A macro calculator helps you determine how many grams of protein, carbohydrates, and fat to eat daily based on your body size, activity level, and specific health goal. Unlike simple calorie counting, macro tracking lets you optimize body composition — building muscle, losing fat, or maintaining weight while supporting energy levels and performance.
This calculator uses the Mifflin-St Jeor equation (1990) — the gold standard for estimating resting metabolic rate — multiplied by an activity factor to give your Total Daily Energy Expenditure (TDEE). Your daily calorie target and macro split are then applied based on your chosen goal.
How Does the Macro Calculator Work?
The calculation happens in three steps:
- BMR (Basal Metabolic Rate): The calories your body burns at complete rest to maintain basic functions like breathing and circulation.
- TDEE: BMR × Activity Factor — accounts for the calories burned through daily movement and exercise.
- Macro split: Your daily calorie target is divided into protein, carbs, and fat percentages based on your goal.
Formula Used
Mifflin-St Jeor BMR:
- Men: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) + 5
- Women: BMR = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) − 161
TDEE = BMR × Activity Factor
| Activity Level | Multiplier |
|---|---|
| Sedentary | × 1.2 |
| Lightly Active (1–3 days/week) | × 1.375 |
| Moderately Active (3–5 days/week) | × 1.55 |
| Very Active (6–7 days/week) | × 1.725 |
| Extra Active (athlete/physical job) | × 1.9 |
Macro splits by goal:
| Goal | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| Weight Loss | TDEE − 500 | 30% | 35% | 35% |
| Maintenance | TDEE | 25% | 50% | 25% |
| Muscle Gain | TDEE + 300 | 30% | 50% | 20% |
Calorie-to-gram conversion: Protein = 4 kcal/g · Carbs = 4 kcal/g · Fat = 9 kcal/g
Benefits of Tracking Macros
- Preserve muscle during weight loss: High protein intake (30%) helps maintain lean mass in a calorie deficit.
- Optimize performance: Adequate carbs fuel workouts; adequate fat supports hormone production.
- Understand food quality: Macro tracking reveals the nutritional composition of your diet beyond just calories.
- Flexibility: Any food can fit your macros (IIFYM — If It Fits Your Macros), making it sustainable long-term.
- Data-driven adjustments: If progress stalls, adjust one macro at a time rather than guessing.
Frequently Asked Questions
What are macros (macronutrients)?
Macronutrients (macros) are the three major nutrients your body needs in large quantities: protein (4 kcal/g), carbohydrates (4 kcal/g), and fat (9 kcal/g). Each plays a distinct role — protein repairs tissue, carbs fuel energy, and fat regulates hormones.
How much protein do I need per day?
For active individuals, 1.6–2.2g per kg of body weight is supported by research for muscle growth and retention. The RDA of 0.8g/kg is a minimum for sedentary adults, not an optimal target for exercisers.
What is TDEE and how is it calculated?
TDEE (Total Daily Energy Expenditure) is the total calories you burn daily. It is calculated using the Mifflin-St Jeor equation for BMR multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (extra active).
What macro split should I use for weight loss?
A 30/35/35 (protein/carbs/fat) split at a 500 kcal deficit from TDEE is a common starting point. High protein preserves muscle; the modest deficit allows ~0.5–1 lb/week of fat loss without excessive metabolic slowdown.
What macro split is best for muscle gain?
A 30/50/20 split at a 300 kcal surplus supports lean bulking. Higher carbs fuel training and recovery; moderate protein (30%) meets the 1.6–2.2g/kg evidence-based range; the small surplus minimizes fat gain.
Can I just track calories without tracking macros?
Yes — calorie balance drives weight change. Macro tracking improves body composition outcomes (more muscle retention, less fat loss from muscle) but is not mandatory for general weight management.
How accurate is this macro calculator?
The Mifflin-St Jeor equation has a standard error of ±10% vs. measured RMR. Treat output as a starting point; adjust by 100–200 kcal after 2–3 weeks of tracking based on actual results.
What is the difference between net carbs and total carbs?
Net carbs = Total carbs − Fiber. Fiber is not digested by the small intestine and does not spike blood sugar. This calculator uses total carbs, which is the standard in most food databases and nutrition labels.