Macro Nutrient Calculator — Protein / Fat / Carb Split for Cut, Maintain, Bulk

Real-world use cases

• Set up a 12-week cut without losing the bench press

  A 35-year-old man at 85 kg / 18% body fat decides to lose 8 kg over 12 weeks. He sets the goal slider to slow cut (-10%) and picks the high-protein preset (40C/30P/30F). The calculator anchors protein at 2.2 g/kg total weight (187 g/day) — high enough that the Helms 2014 meta-analysis says lean mass loss should be under 15% of total weight loss. He swaps the carb source toward rice and oats around training and the fat source toward salmon and avocado on rest days. Twelve weeks later the scale reads 77 kg, his 1RM bench is down only 5% instead of the 15-20% an "eat less" diet would produce, and the macro split made the discipline mechanical instead of willpower-driven.

• Switch a frustrated dieter from low-fat to keto

  A 42-year-old woman has lost and regained 6 kg three times on conventional 1500 kcal low-fat plans. She tries keto for 8 weeks. The calculator's keto preset gives her 5C/30P/65F at 1800 kcal (her TDEE × 0.85). The protein floor at 1.8 g/kg stops the muscle loss that wrecked her previous attempts. The 65% fat target finally produces real satiety — avocado at breakfast, salmon and olive oil at lunch, eggs and cheese at dinner. The sanity-check warning (low fat <20%) flags her old plan as the actual culprit: her previous diets were starving her of fat AND putting her body in a calorie deficit simultaneously. Eight weeks in she's down 5 kg and stays there.

• Plan a lean-bulk for a teen lifter without getting fat

  A 17-year-old lifter at 65 kg / 13% body fat wants to add muscle for a powerlifting meet 6 months out. He picks slow bulk (+10%) with the high-protein preset and supplies his body-fat number so the calculator switches to Katch-McArdle. Lean mass = 56.5 kg, so protein anchors at 56.5 × 2.4 = 135 g (the lean-mass scaling is more accurate than total-weight scaling at this body composition). Total target lands at 3100 kcal, carbs at 388 g around training to fuel his 5x5 / RPE work. Six months later he weighs 71 kg with body fat at 14% — net gain of 5.5 kg lean and only 0.5 kg fat, exactly what a +10% surplus is supposed to deliver, instead of the +500-kcal "dirty bulk" that adds 8 kg of which 5 kg is fat.

• Rescue a vegan athlete whose recovery has tanked

  A 28-year-old vegan triathlete has been dragging through her long runs and feels her recovery is off. She enters her data and the calculator targets 2.0 g/kg protein × 62 kg = 124 g for her endurance training maintenance. She maps her current intake and discovers she's at 78 g — the meat-free shift cut her protein 40% without her noticing. The meal example shows how to hit 124 g on plants (tofu, tempeh, lentils, seitan, plus a 30 g pea-protein shake). Inside 3 weeks her long-run pace recovers and morning fatigue lifts — not magic, just the macro target a coach would have flagged on day one.

• Cycle macros for an office worker doing 4 strength days

  A 31-year-old project manager lifts four times a week at lunchtime and works a desk job otherwise. He runs the calculator twice — once on training days with activity 'moderate' (gives 2450 kcal), once on rest days with 'light' (gives 2200 kcal). He keeps protein constant at 180 g (no point cycling protein), cycles carbs +60 g on lift days and fat +25 g on rest days. Over 16 weeks he holds 85 kg body weight but adds 4 cm to his arms and 8 kg to his chest press — body recomposition, the slowest but most durable training outcome, made possible by giving each day the carbs it specifically needs.

Common pitfalls

• Maxing the deficit at -30% or worse to "speed it up". Anything beyond -25% wrecks lean mass retention (Garthe 2011), tanks training quality, and gives back the loss the moment normal eating returns. The tool flags >25% deficits in yellow on purpose — slow cuts win.

• Trusting the protein number without checking the food label. 100 g of "chicken breast" raw weighs ~30% less after cooking and is ~23 g protein per cooked 100 g, not per raw 100 g. Hitting the protein target requires weighing cooked or applying the raw-to-cooked yield, otherwise you'll undereat protein by 25-30%.

• Picking keto because "it worked for someone on Instagram" without checking the fat number. Keto only works if you actually eat 60-75% calories from fat — most failed keto attempts are accidentally low-fat AND low-carb, which is just starvation, no ketosis, and zero satiety advantage.

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