About the Macro Calculator

This Macro Calculator translates your daily calorie target (derived from Mifflin-St Jeor BMR × activity, adjusted for goal) into grams of protein, carbohydrate, and fat per day. The three macronutrients supply energy in different densities: protein and carbohydrate provide 4 kcal/g, while fat provides 9 kcal/g. Alcohol supplies 7 kcal/g but is not treated as a training macro.

Three goal-specific splits are offered: Cut 40/30/30 (higher protein to preserve lean mass in a deficit), Maintain 30/40/30 (moderate protein, moderate carbs, moderate fat), and Bulk 30/45/25 (lower protein relative to calories, higher carbs to fuel training). These align with International Society of Sports Nutrition (ISSN) 2017 position stands.

For active individuals, ISSN recommends 1.6-2.2 g protein per kg body weight per day (the upper end for those in a deficit or building muscle). Endurance athletes need 5-10 g/kg/day carbs; strength athletes 4-7 g/kg/day. Fat should not fall below 0.5-1.0 g/kg/day to avoid hormonal disruption (especially in women, where low fat intake disrupts menstrual cycles).

How It Works

Step 1: compute BMR via Mifflin-St Jeor, multiply by activity factor (1.2-1.9) for TDEE.

Step 2: adjust for goal — cut subtracts 500 kcal, bulk adds 500, maintain keeps TDEE.

Step 3: apply macro split (percentage of total calories):

Goal      Protein  Carbs   Fat
Cut       40%      30%     30%
Maintain  30%      40%     30%
Bulk      30%      45%     25%

Step 4: convert calories to grams using the Atwater factors:

Protein: grams = kcal / 4
Carbs:   grams = kcal / 4
Fat:     grams = kcal / 9

These factors come from Atwater’s 1896-1904 bomb-calorimetry studies, refined by Merrill and Watt (USDA Handbook 74, 1973). They are accurate within ~5% for whole foods; processed foods may differ due to fibre, sugar alcohols, and resistant starch.

For example, at 2,400 kcal with a cut split: 960 kcal protein = 240 g, 720 kcal carbs = 180 g, 720 kcal fat = 80 g.

Worked Examples

A 75 kg man, 178 cm, 30 years, moderately active (TDEE 2,661 kcal), choosing Cut:

Target = 2,661 - 500 = 2,161 kcal/day
Protein 40% = 864 kcal / 4 = 216 g (2.9 g/kg - high, reserved for trained athletes)
Carbs 30% = 648 kcal / 4 = 162 g
Fat 30% = 648 kcal / 9 = 72 g

For most non-athletes, 1.6-2.2 g/kg protein suffices (~120-165 g for a 75 kg man). Consider Maintain split or custom ratios if cut-split protein feels excessive.

A 62 kg woman, 165 cm, 35 years, lightly active (TDEE 1,808 kcal), choosing Maintain:

Target = 1,808 kcal/day
Protein 30% = 542 kcal / 4 = 136 g (2.2 g/kg - upper ISSN range)
Carbs 40% = 723 kcal / 4 = 181 g
Fat 30% = 542 kcal / 9 = 60 g

For a Bulk at 3,000 kcal/day (75 kg man): Protein 30% = 900 kcal = 225 g, Carbs 45% = 1,350 kcal = 338 g, Fat 25% = 750 kcal = 83 g.

When to Use This Tool

Plan daily macros for a bodybuilding cut, recomp, or bulk phase.
Translate calorie targets into food choices for meal-prep apps (MyFitnessPal, Cronometer, MacroFactor).
Set protein targets for muscle preservation during weight loss (ISSN 1.6-2.2 g/kg).
Adjust carb intake for endurance training (5-10 g/kg/day during heavy weeks).
Plan keto or low-carb modifications (e.g., 20/10/70 P/C/F for <50 g carbs).
Track macros alongside strength training to optimise body composition.
Set minimum fat intake (≥0.5-1.0 g/kg) to protect hormonal function.

Limitations & Disclaimer

Macro calculations estimate needs using population-average equations and may differ from your individual response by 100-300 kcal/day. Atwater factors are approximations; processed foods, fibre, and resistant starch shift actual energy yield by 5-10%. Micronutrient needs (vitamins, minerals, fibre) are not captured. This tool is not medical advice; consult a registered dietitian for individualised plans, especially with medical conditions. See our disclaimer for full terms.

Frequently Asked Questions

Which macro split should I choose?

Cut 40/30/30 preserves lean mass in a deficit via high protein. Maintain 30/40/30 is balanced for most. Bulk 30/45/25 prioritises carbs to fuel training. For keto or low-carb, use custom ratios (e.g., 25/5/70). The Academy of Nutrition and Dietetics accepts protein 10-35%, carbs 45-65%, fat 20-35% for general health.

How much protein do I really need?

The RDA is 0.8 g/kg/day (National Academies). Active individuals need 1.2-1.7 g/kg (ISSN 2017), endurance athletes 1.2-1.4 g/kg, strength athletes 1.6-2.2 g/kg. Protein above 2.2 g/kg/day shows diminishing returns unless in a steep deficit or on anabolic agents.

Are the Atwater factors (4/4/9) accurate?

Within ~5% for whole foods. Fibre contributes ~2 kcal/g; sugar alcohols vary (0-3 kcal/g); resistant starch resists digestion. The USDA FoodData Central database uses refined factors for individual foods.

Can I track macros without a food scale?

Approximately — using hand portions (palm = ~20-30 g protein, cupped hand = ~20-30 g carbs, thumb = ~7-12 g fat) per Precision Nutrition. For precise tracking, a kitchen scale ($15-30) is essential. Apps like Cronometer and MacroFactor simplify tracking with barcode scanning.

What if I’m vegetarian or vegan?

Plant proteins are typically less bioavailable (PDCAAS 0.5-0.9 vs animal 1.0). Aim for 1.6-2.2 g/kg/day from varied sources (legumes, tofu, tempeh, peas, nutritional yeast). Combine complementary proteins (rice + beans) within 24 hours for a complete amino acid profile.

Do alcohol calories count?

Yes — alcohol provides 7 kcal/g and counts toward total daily intake, but is not a “macro” in the protein/carb/fat sense. Track separately and subtract from carb or fat allowance. Heavy drinking impairs protein synthesis, sleep, and recovery.

Last updated: September 9, 2026 · Author: HT99 Tools Editorial Team