Protein / Macro Calculator

Understanding Macronutrients

Macronutrients — protein, carbohydrates, and fat — are the three main categories of nutrients that provide energy. Protein and carbohydrates each provide 4 calories per gram, while fat provides 9 calories per gram. Tracking your macros allows you to go beyond simply counting calories, giving you a more precise nutritional approach to achieving your specific body composition and performance goals. Our free macro calculator generates your personalised daily targets instantly using the Mifflin-St Jeor equation for TDEE and evidence-based macro ratios for each goal.

All calculations run in your browser with no data ever sent to a server.

How to Calculate Your Daily Macros Online

1. Select Metric or Imperial — choose your unit system using the toggle.
2. Choose your biological sex — the Mifflin-St Jeor BMR formula uses different constants for male and female.
3. Enter age, height, and weight — use the number inputs or sliders.
4. Select activity level — choose from the dropdown; this multiplies your BMR to calculate TDEE.
5. Choose your goal — Cut (−500 kcal deficit for fat loss), Maintain (at TDEE), or Bulk (+300 kcal surplus for muscle gain).
6. Read your macros — the result panel shows grams per day for protein, carbs, and fat, their caloric contribution, a proportion bar, and your underlying BMR and TDEE.

How the Macro Calculator Works Technically

The calculator implements the Mifflin-St Jeor equation for BMR, multiplies by a PAL activity factor for TDEE, applies a goal-based calorie adjustment, then distributes calories using goal-specific macro ratios. Protein is set first (in g/kg), fat is set second (in g/kg), and carbohydrates fill the remaining calories.

Macronutrient Roles — 6 Key Facts

• Protein builds and preserves muscle: Every gram of muscle protein synthesised requires dietary amino acids. Without adequate protein — especially during a calorie deficit — your body catabolises muscle tissue for energy. 1.6–2.4g/kg is the evidence-supported range for active individuals.
• Protein has the highest thermic effect: 20–30% of protein calories are burned during digestion — significantly more than carbohydrates (5–10%) or fat (0–3%). This means high-protein diets burn more calories from food processing alone.
• Carbohydrates fuel high-intensity training: Muscle glycogen — stored from dietary carbohydrates — is the primary fuel for anaerobic effort above 70–75% of VO2 max. Low carbohydrate intake impairs training intensity and volume, reducing the stimulus for muscle growth. Use our Calorie Calculator to cross-check your total intake.
• Fat is essential for hormones: Dietary fat is required for the synthesis of testosterone, oestrogen, and cortisol. Never reduce fat below 0.5g/kg even during aggressive cuts — hormonal disruption at very low fat intakes impairs recovery, libido, and immune function.
• Total calories determine weight direction: Regardless of macro ratio, fat loss requires a calorie deficit and weight gain requires a surplus. Macros determine the quality and composition of that weight change — whether you gain muscle or fat, whether you preserve muscle during a deficit.
• Consistency beats perfection: Hitting your protein target is the most important daily priority. Being within ±5g of protein and ±10g of carbs and fat represents excellent adherence. Use our BMR Calculator to periodically recalculate your targets as your body weight changes.

Cutting vs Bulking — Which Should You Do?

The right phase depends on your current body composition and goals. If your body fat is above 20% (men) or 28% (women), cutting first will improve your body composition and insulin sensitivity before attempting a bulk. If you are already lean with a solid strength base, a controlled bulk of 0.25–0.5% of body weight per week builds muscle efficiently. Most experienced lifters alternate phases: cut until lean, bulk for 3–6 months, cut again to reveal the gained muscle. Beginners can often achieve simultaneous fat loss and muscle gain (body recomposition) for their first 6–12 months regardless of phase.

Adjusting Macros Over Time

As you lose or gain weight, your TDEE changes — recalculate your macros every 4–8 weeks to account for your new body weight. Most people need to reduce calories by 50–100 kcal per week during a cut to continue losing at a steady rate. Track your weekly average weight trend rather than daily fluctuations, and adjust only after at least 2 weeks of stable data to avoid overreacting to water weight changes.

Privacy and Security

The Macro Calculator runs entirely in your browser using JavaScript arithmetic — no data is transmitted to ToollyX servers at any point. Your age, height, weight, activity level, goal, and macro targets never leave your device. This is safe for personal nutrition planning, clinical weight management programmes, and sensitive dietary health data you prefer not to store on external services.

✓Verified by ToollyX Team · Last updated June 2026