Case 1
- Sex
- Male
- Age
- 30
- Weight
- 80kg
- Height
- 180cm
- Activity level
- Moderately active — 3–5 sessions (× 1.55)
- Goal
- Lose fat (−15 %)
- Protein per kg of body weight
- 2g/kg
- Fat as a share of calories
- 25%
280g/d
Open with these valuesMacro Calculator
280g/d
Result: 280 g/dProtein is set by your body weight, fat by a percentage of your calorie target — carbohydrate gets whatever is left, which is why it swings most when the goal changes. The result here is that remainder in grams per day; the table below shows the protein and fat that go with it.
The numbers at a glance
Held fixed: Sex Male, Age 30, Weight 80.0 kg, Height 180.0 cm, Activity level Moderately active — 3–5 sessions (× 1.55), Goal Lose fat (−15 %), Protein per kg of body weight 2.0 g/kg.
| Fat as a share of calories (%) | Result (g/d) |
|---|---|
| 15 | 338 |
| 20 | 309 |
| 25Your value | 280 |
| 30 | 250 |
| 35 | 221 |
Worked examples
Case 2
- Sex
- Female
- Age
- 35
- Weight
- 65kg
- Height
- 165cm
- Activity level
- Lightly active — 1–3 sessions (× 1.375)
- Goal
- Lose fat (−15 %)
- Protein per kg of body weight
- 2g/kg
- Fat as a share of calories
- 30%
145g/d
Open with these valuesCase 3
- Sex
- Male
- Age
- 30
- Weight
- 80kg
- Height
- 180cm
- Activity level
- Moderately active — 3–5 sessions (× 1.55)
- Goal
- Bulk (+20 %)
- Protein per kg of body weight
- 1.8g/kg
- Fat as a share of calories
- 30%
435g/d
Open with these valuesHow it's calculated
carbs g = (target kcal − kg·g/kg·4 − target·fat%) ÷ 4
- StepEnter your body data and pick the activity level of a normal week.
- StepPick the goal — it shifts the calorie target by a percentage, not a flat number.
- StepSet protein per kilogram (1.4–2.0 g/kg covers most active people).
- StepSet the fat share; 20 % is the sensible floor, 25 % the default here.
- ResultRead the carbohydrate grams — everything the other two did not claim.
What this number means
The figure on this page is a target, not a measurement of your body: how many grams of carbohydrate a day are left once protein and fat have taken their share of an estimated calorie budget. It says nothing about which foods supply them. Follow the default settings through the chain. A 30-year-old man at 80 kg and 180 cm has a resting energy figure of 1780 kcal from the Mifflin-St Jeor equation. The moderately active multiplier of 1.55 raises that to 2759 kcal, and the fat-loss goal of minus 15 percent puts the target at 2345 kcal. Protein at 2 g per kilogram of body weight is 160 g, worth 640 kcal at 4 kcal per gram. Fat at 25 percent of the target is 586 kcal, which is 65 g at 9 kcal per gram. The 1119 kcal that neither has claimed, divided by 4, gives the 280 g of carbohydrate shown. Read it as one plausible split of an estimated budget, and pay more attention to which way it moves when you change a field than to the last digit. The limitation worth holding on to is structural: because carbohydrate is the remainder, it inherits the error of every step before it. A resting figure that is off, or an activity level picked one notch too generously, does not spread itself across three macros — it lands on this one number in full.
Carbohydrate is the remainder
Protein is set by body weight and fat by a share of the calorie target, so carbohydrate takes whatever those two leave. That is why it swings most when the goal changes.
Why protein is set per kilogram
Protein requirements track lean mass rather than energy intake, so a share of calories would fall exactly when the deficit is largest. The ISSN position stand supports 1.4–2.0 g/kg for active people.
The activity and goal factors are conventions
The activity multipliers come from the nutrition literature and the goal adjustment from the old calculator, neither from the cited source. Both are printed in the option labels so the assumption stays visible.
Consistency beats precision on a single day
Within about 10 g on each macro, most days, is plenty. Labels carry their own tolerance, portions vary, and daily expenditure is not constant.
Commonly misread
The page leaves protein and fat out.
Both are in the table above for the default body, at 160 g of protein against every goal. Carbohydrate is the figure shown because it is the one you cannot work out in your head.
Changing the goal moves all three macros equally.
Protein is fixed to body weight and fat to a percentage, so the adjustment lands almost entirely on carbohydrate. It is 280 g when cutting against 357 g when maintaining, with protein at 160 g in both.
Zero carbohydrate grams means the calculator has failed.
It means protein and fat together already claim the whole calorie target, leaving nothing for the third. A different protein factor or fat share moves the remainder off zero.
Reference table
| Goal | Calorie target | Protein | Fat | Carbohydrate |
|---|---|---|---|---|
| Lose fat fast (−25 %) | 2069 kcal | 160 g | 57 g | 228 g |
| Lose fat (−15 %) | 2345 kcal | 160 g | 65 g | 280 g |
| Maintain (0 %) | 2759 kcal | 160 g | 77 g | 357 g |
| Lean bulk (+10 %) | 3035 kcal | 160 g | 84 g | 409 g |
| Bulk (+20 %) | 3311 kcal | 160 g | 92 g | 461 g |
Questions
What are macros?
Protein, fat and carbohydrate — the three nutrients that carry energy, at 4, 9 and 4 kcal per gram. The calorie total decides whether your weight moves; the split shapes what the body does with the change.
Why does this page show carbohydrate rather than all three?
Because carbohydrate is the only one you cannot work out in your head. Protein is your weight times a factor, fat is a percentage of the target, and carbohydrate is whatever those two leave — the table above lists all three for the default body.
Why is protein set per kilogram instead of as a percentage?
Because protein requirements track lean mass, not energy intake. If protein were a share of calories, cutting calories would cut protein exactly when it matters most. The ISSN position stand supports 1.4–2.0 g/kg for active people.
How much fat should I eat?
At least about 20 % of calories — below that, hormone production and fat-soluble vitamin absorption suffer. Above that floor, the split between fat and carbohydrate is mostly preference and training style.
Why do my carbs change so much when I change the goal?
Because carbohydrate takes whatever is left. Protein is fixed to body weight and fat to a percentage, so the goal adjustment lands almost entirely on carbohydrate: 280 g when cutting against 357 g when maintaining, with protein at 160 g in both.
How precisely do I need to hit these numbers?
Within about 10 g on each macro, most days, is plenty. Labels carry their own tolerance, portions vary, and daily expenditure is not constant — consistency across a week beats precision on any single day.
Sources and last check
Information, not medical advice.