How the macro calculator works
The calculator works in two steps. First it sets a daily calorie target. It estimates your resting energy with the Mifflin–St Jeor equation, multiplies by your activity factor to get maintenance calories, then adds or removes calories for your goal (about 500 kcal a day for 1 lb a week). If you already know your number, type it into “Own calorie target” and the calculator skips this step.
Second, it splits those calories between the three macronutrients using the percentages of your diet style, and converts each share to grams:
Carbohydrate (g) = calories × carbohydrate % ÷ 4
Fat (g) = calories × fat % ÷ 9
The 4 and 9 are the standard Atwater energy factors used on nutrition labels: a gram of protein or carbohydrate gives about 4 kcal and a gram of fat about 9 kcal.
Diet style presets
| Preset | Carbs | Protein | Fat | Best for |
|---|---|---|---|---|
| Balanced | 50% | 20% | 30% | Most people; sits inside all official ranges |
| Low fat | 60% | 20% | 20% | People who prefer starchy foods, endurance training |
| High protein | 35% | 35% | 30% | Fat loss while keeping muscle, staying full |
| Zone | 40% | 30% | 30% | A middle ground many gyms use |
| Low carb | 25% | 35% | 40% | People who feel better with fewer starches |
| Keto | 5% | 20% | 75% | Very low carb eating (about 20–50 g a day) |
The US National Academies set Acceptable Macronutrient Distribution Ranges (AMDR) for adults: 45–65% of calories from carbohydrate, 10–35% from protein and 20–35% from fat. The balanced and low fat presets fall inside them. Low carb and keto deliberately go outside, so the calculator points that out. That does not make them unsafe for healthy adults, but anyone with diabetes, kidney disease or another condition should get advice before a big change.
Worked examples
Example 1: balanced, losing weight. A 30-year-old woman, 5 ft 5 in and 150 lb, moderately active, wants to lose 1 lb a week.
- BMR = 10 × 68.0 + 6.25 × 165.1 − 5 × 30 − 161 = 1,401 kcal. Maintenance = 1,401 × 1.55 = 2,172 kcal.
- Target = 2,172 − 500 = 1,672 kcal.
- Carbs 50%: 836 kcal ÷ 4 = 209 g. Protein 20%: 334 kcal ÷ 4 = 84 g. Fat 30%: 502 kcal ÷ 9 = 56 g.
Her protein is 84 ÷ 68 = 1.2 g per kg. Switching to the high-protein preset raises it to 146 g (2.1 g/kg) with carbs at 146 g and fat unchanged at 56 g, which many people find more filling while dieting.
Example 2: keto. A man eating 2,800 kcal a day on the keto preset gets carbs 140 kcal ÷ 4 = 35 g, protein 560 kcal ÷ 4 = 140 g and fat 2,100 kcal ÷ 9 = 233 g.
Example 3: per meal. On 2,400 kcal with the zone split (40/30/30), the day is 240 g carbs, 180 g protein and 80 g fat. Over four meals, each one is about 60 g carbs, 45 g protein and 20 g fat.
How much protein, carbohydrate and fat do you need?
Percentages are convenient, but protein is better judged per kilogram of body weight. The adult RDA is 0.8 g/kg, a minimum to avoid deficiency. A 2016 joint position from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine suggests 1.2–2.0 g/kg for athletes. The calculator shows your protein in g/kg and warns if it drops below 0.8 or climbs well past what research supports. For a target based on your training, use the protein calculator.
Carbohydrate is your main fuel for hard exercise. People who train for long periods need more, while less active people can do well on less. Fat should rarely fall below about 20% of calories, because you need it for hormones and to absorb vitamins A, D, E and K.
Tips for tracking macros
- Get the calories right first. The split only changes where the calories come from. Use the calorie calculator or the TDEE calculator if you are unsure.
- Hit protein, then stay near the rest. Being within 5–10 g of each target is plenty.
- Read labels per serving. Nutrition labels list grams of each macro per serving; multiply by how many servings you actually eat.
- Weigh food for a week or two. It quickly teaches you what 30 g of protein or 50 g of carbs looks like.
- Adjust from results. If your weight trend does not move as planned after 2–3 weeks, change total calories by 100–200 kcal and keep the same split.
Limits
These are estimates for healthy adults. They are not designed for children, pregnancy, eating disorders, or medical diets such as those for kidney disease or diabetes. If that applies to you, ask a doctor or registered dietitian. To plan a weight-loss date, see the calorie deficit calculator.