How this works
Macros (short for macronutrients) are the three energy-providing nutrients: protein, carbohydrates and fat. Once you know your daily calorie target — from a TDEE calculation, a deficit goal, or a coach's prescription — splitting it across the three macros gives you concrete grams to hit each day. The math is simple: protein and carbs are 4 calories per gram, fat is 9 calories per gram, so once you pick a percentage split (say 30% protein / 40% carbs / 30% fat) the gram targets fall out of straightforward division. Which split is "right" depends on what you're training for and personal preference. The most defensible default for an active adult on a normal diet is roughly 1.6–2.2 g protein per kg of bodyweight (preserves muscle in a deficit, supports growth in a surplus), 0.8–1.0 g fat per kg as a floor for hormone health, and the rest as carbs to fuel training and brain function. That works out to something like a 30/40/30 split for most people. Endurance athletes lean carb-heavy (often 50–60%); low-carb and keto practitioners drop carbs to 20% or under and lift fat to 50–70%. Bodybuilders in a cut often hit 40% protein. The presets in the calculator above cover the common bands; the custom mode lets you set arbitrary percentages. Three practical points. (1) Hitting macros isn't about precision; it's about consistency. Being within ±5g protein and ±10g carbs/fat over a week is more than enough for any non-elite goal. Don't weigh broccoli. (2) The 4 / 4 / 9 cal/g constants are nominal — actual metabolisable energy varies slightly by food (the Atwater system rounds these for labelling), but the difference doesn't matter at the calorie totals most people target. (3) Fibre is a carbohydrate that mostly doesn't metabolise, so some people use "net carbs" (total carbs minus fibre) when planning. The calculator uses total carbs because that's how nutrition labels report unless you're specifically tracking net carbs for keto.
The formula
Constants: protein and carbs are 4 cal/g, fat is 9 cal/g. The Atwater general factors round these from research values (4.0, 4.0, 9.0); food labels worldwide use the same constants. Percentages should sum to 100; the calculator normalises if you go over or under.
Example calculation
- Daily target: 2,200 kcal, balanced split (30% P / 40% C / 30% F).
- Protein: (2200 × 30%) / 4 = 660 / 4 = 165 g
- Carbs: (2200 × 40%) / 4 = 880 / 4 = 220 g
- Fat: (2200 × 30%) / 9 = 660 / 9 ≈ 73 g
Frequently asked questions
Which macro split should I pick?
Default to "Balanced" (roughly 30/40/30) unless you have a specific reason to deviate. Pick "High protein" if you're cutting (preserves muscle) or trying to build muscle while in a calorie surplus. Pick "Low carb" if you respond better to lower-carb diets for satiety or have insulin sensitivity reasons. Pick "Keto" only if you're following a true ketogenic protocol — it requires sustained adherence and isn't a small lifestyle tweak. Pick "Endurance" if you're training 8+ hours/week of cardio and need the carb fuel. The "right" split for body composition is usually less important than total calories and protein floor; the macros that surround the protein matter mostly for energy and adherence.
How do I know my daily calorie target?
Use the calorie calculator on this site (related links below). It estimates your BMR via Mifflin-St Jeor, multiplies by an activity factor to get TDEE (your maintenance), then applies a 500 kcal deficit for fat loss or a 300 kcal surplus for lean gain. Plug that TDEE-based number into the macro calculator. As a sanity check, most adult fat-loss targets land between 1,400 and 2,000 kcal/day; maintenance is usually 1,800–2,800; bulk targets are 2,200–3,500. If your number is far outside those bands, double-check the activity multiplier and the underlying weight/height inputs.
Should I track macros or just calories?
Calories first, macros second — this is the consensus in evidence-based fitness (look at any review by Eric Helms, Alan Aragon or Layne Norton). For weight management, calorie balance does about 80% of the work. For body composition (muscle vs fat at a given weight), protein matters most — getting enough is critical. Carb/fat split matters mostly for training performance and adherence. So: if you're new to tracking, just count calories and aim for a protein floor (~1.6 g/kg). If you're hitting a plateau, dialing macros tighter helps. If you have a specific physique or sport goal (lean bulk, marathon, weight class), full macro tracking pays off.
My percentages don't add up to 100 — what happens?
The calculator normalises them so the total grams cover your full calorie target. If you enter 30/35/30 (sum 95%), the calculator scales each up by 100/95 ≈ 1.053 — so you'd get 31.6%/36.8%/31.6% effectively. If you enter 40/40/40 (sum 120%), it scales each down. Practically: enter percentages that feel right, the math works out as long as the relative ratios make sense. A warning shows if your sum is far from 100 in case you mistyped.