How many carbs you should eat per day, in the MacroDiet formula, is whatever is left once protein and fat have taken their share: carbs = (calories − protein × 4 − fat × 9) ÷ 4. There is no carbohydrate tier to choose. The number moves when the calorie target moves, when the protein tier moves, or when the diet style changes fat's share of the remainder.
That is a deliberate design, and this article explains it — then puts the result against the published reference range and the ranges sports nutrition uses for people who train.
Carbs are the remainder
Every step before carbohydrate is fixed by a rule: energy from expenditure and goal, protein from body weight, fat from a style share with a floor. Carbohydrate is the only macro with no rule of its own, because it is the only one that can safely be the flexible part. Protein has a job the other two cannot do, fat has a floor, and carbohydrate is the energy that fills the space between them.
A 75 kg person at 2,000 kcal, moderate protein, balanced style:
| Step | Arithmetic | Result |
|---|---|---|
| Protein | 75 × 1.6 | 120 g = 480 kcal |
| Fat | (2,000 − 480) × 0.35 ÷ 9 | 59 g = 531 kcal |
| Carbohydrate | (2,000 − 480 − 531) ÷ 4 | 247 g = 989 kcal (49% of energy) |
In plain terms: you do not pick a carb number; the other three decisions pick it for you.
Ranges by activity (table)
The Institute of Medicine sets an acceptable range of 45–65% of energy from carbohydrate for adults and an RDA of 130 g/day.1 Sports-nutrition guidance is written per kilogram of body weight instead, because the training load, not the calorie total, is what drives the need; the review by Burke and colleagues frames carbohydrate for athletes around total daily intake and its timing relative to sessions, with in-session targets of 30–60 g/h for longer events and up to 90 g/h beyond about 2.5 hours.2
The daily ranges below are the ones commonly quoted in that literature; they are a research lead in our grounding notes, not a MacroDiet rule, and are shown to give the remainder some context:
| Situation | Typical daily carbohydrate | 75 kg person |
|---|---|---|
| Reference range (IOM AMDR)1 | 45–65% of energy | 225–325 g at 2,000 kcal |
| Adult RDA1 | 130 g | 130 g |
| Lifting-focused training (commonly quoted) | 3–4 g/kg | 225–300 g |
| Endurance training (commonly quoted) | ≥ 6 g/kg | ≥ 450 g |
| Low-carb (working definition) | < 200 g or about 30% of energy | < 200 g |
| Keto (MacroDiet ceiling) | 30 g | 30 g |
Note what the table implies: the balanced remainder of 247 g for a 75 kg lifter falls inside both the reference range and the commonly quoted lifting range without any carbohydrate-specific rule. An endurance athlete's number does not, which is a reason to choose the low-fat style or a higher calorie target rather than to expect a carb rule to appear.
Low-carb and keto thresholds
Two thresholds matter in the algorithm.
Low-carb is a style, not a ceiling. It gives fat 50% of the post-protein calories (versus 35% balanced), and carbohydrate falls as a result. At the 2,000 kcal example above the low-carb remainder is 191 g — under the 200 g working definition, but only because the calorie total is moderate. At 3,000 kcal the same style produces 315 g, which nobody would call low-carb. The style sets a ratio; the calorie target sets the grams.
Keto is a ceiling. Carbohydrate is fixed at 30 g (KETO_CARB_CEILING_G) whatever the calories, and fat becomes the remainder. 30 g is stricter than the 50–60 g figure many keto guides use; the app treats it as an upper limit rather than a number to aim at, and counts fibre inside it.
How the diet-style setting changes the split
Because carbohydrate is the remainder, the style setting reaches it only through fat's share:
| Style | Fat share of post-protein calories | Carb share of post-protein calories | Carbs at 2,000 kcal, 75 kg |
|---|---|---|---|
| Low-fat | 20% → lifted to the floor | ≈ 73% after the floor | 279 g |
| Balanced | 35% | 65% | 247 g |
| Low-carb | 50% | 50% | 191 g |
| Keto | remainder | fixed 30 g | 30 g |
Changing the protein tier has the same kind of effect: each extra 0.4 g/kg of protein for a 75 kg person removes 120 kcal from the remainder, roughly 20 g of carbohydrate on the balanced style.
In plain terms: to move carbs, change calories, protein or style — the carb number itself is never edited by the algorithm.
The short version
Carbohydrate in MacroDiet is the remainder after protein and fat, divided by 4. The published reference range is 45–65% of energy with an RDA of 130 g;1 training guidance scales the total with load and times it around sessions.2 Low-carb is a style that gives fat half the remainder; keto is a 30 g ceiling with fat as the balancing macro. Try the macro calculator to see the remainder move as you change the inputs.
Educational overview only — not medical advice. Zyra is a training and nutrition tracking tool; the numbers here are the algorithm's rules and published reference values, not an individual prescription.