The Macro Calculator turns your body measurements, activity level, and goal into a daily calorie target split into protein, carbohydrate, and fat grams using the macro split you prefer. It accepts metric or imperial units: enter weight and height in pounds and inches and it converts them before calculating.
How It Works
Calories come from the Mifflin-St Jeor equation (10 x weight in kg + 6.25 x height in cm - 5 x age, plus 5 for men or minus 161 for women) multiplied by an activity factor from 1.2 (sedentary) to 1.9 (very active) to give TDEE. The goal then adjusts the target: cut and lose subtract 500 kcal, lean bulk adds 200, bulk and gain add 500, and maintain leaves TDEE unchanged. The chosen macro preference splits the calories, and grams follow from the energy densities: 4 kcal per gram of protein and carbohydrate, 9 per gram of fat.
Macro splits used
| Preference | Protein | Carbohydrate | Fat | |---|---|---|---| | Balanced | 30% | 40% | 30% | | Low carb | 40% | 20% | 40% | | High protein | 40% | 40% | 20% | | Low fat | also available | | |
Parameters
| Input | Required | Meaning | |---|---|---| | Gender, age | Yes | Select the Mifflin-St Jeor constant and age term | | Weight and height | Yes | Metric, or pounds/inches with the imperial setting | | Activity level | Yes | Sedentary, light, moderate, active, or very active | | Goal | Yes | Cut, lose, maintain, lean bulk, bulk, or gain | | Macro preference | No | Balanced, low carb, high protein, or low fat |
Worked example
Take the calorie target of 2,000 kcal with the balanced split: protein takes 30% (600 kcal, 150 g), carbohydrate 40% (800 kcal, 200 g), and fat the remaining 30% (600 kcal, about 67 g). On the low-carb split the same 2,000 kcal becomes 200 g protein (40%), 100 g carbohydrate (20%), and about 89 g fat (40%): same calories, very different plates. This is the essential macro insight: splits redistribute fullness, training fuel, and food choices, but the calorie target, set by the goal adjustment, is what drives weight change.
Choosing a split you can keep
High protein suits cutting phases and anyone training hard, because protein protects muscle and satiety when calories are scarce. Low carb suits people who prefer fat-rich foods and stable energy, at the cost of some high-intensity training fuel. Balanced is the default most people can sustain socially and nutritionally. The differences between splits at equal calories are second-order for body composition in the research; adherence over months dominates. Pick the split whose meals you would still enjoy in week ten.
How precise is any of this?
The equation's individual error is around plus or minus 10%, activity selection is a guess dressed as a category, and food labels carry their own tolerance. Treat the output as the centre of a range: run the target for two to three weeks, compare the weight trend with the goal (the calculator's cut assumes roughly half a kilogram a week at a 500 kcal deficit), and adjust by 100 to 200 kcal rather than recalculating from scratch. Imperial inputs are converted with the standard factors (0.4536 kg per pound, 2.54 cm per inch), so a 180 lb, 5 ft 11 in entry is computed as about 81.6 kg and 180.3 cm.
Limitations
The calculator does not account for body-composition measurement (a lean-mass-based formula would need body-fat percentage), metabolic conditions, medications, pregnancy, or athletic periodization. Macro percentages are fixed presets, not personalized prescriptions, and medical nutrition decisions belong with a clinician or dietitian.
Adjusting when the scale disagrees
If two to three consistent weeks show weight moving the wrong way or not moving, the inputs, not the arithmetic, are the suspects. The usual culprits in order: activity level chosen one notch too high, untracked cooking oils and drinks adding 200 to 400 unlogged calories, and weekend intake quietly averaging the deficit away. Fix one variable at a time, changing the calorie target by 100 to 200 kcal or re-anchoring protein and letting the other macros float, and give the change another two weeks. Recalculating after every weigh-in manufactures noise; the calculator gives you a starting hypothesis, and your trend data is the peer review.
Frequently Asked Questions
Should protein be set by percentage or by body weight?
Body weight is the better anchor for athletes (commonly 1.6 to 2.2 g per kg). The percentage presets here approximate that for typical calorie targets; at very low or very high calories, check the gram figure the percentage produces against your weight.
Why does the cut subtract 500 kcal?
It is the conventional deficit approximating half a kilogram of fat loss per week (roughly 3,500 kcal of cumulative deficit). Larger deficits lose faster but cost more muscle, energy, and adherence.
Do I need to hit the grams exactly every day?
No. Think in weekly averages and a protein floor you rarely miss. Day-to-day variation of 5 to 10% in carbs and fat is normal eating, not a failed plan.