How the macro calculator works
The calculator works in four steps. Each one uses a published equation, so you can check the numbers yourself.
1. Basal metabolic rate (BMR). This is the energy your body uses at complete rest. By default we use the Mifflin-St Jeor equation (Mifflin et al., American Journal of Clinical Nutrition, 1990). A review by the American Dietetic Association found it the most reliable of the common equations for healthy adults (Frankenfield et al., 2005).
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
If you enter your body fat percentage, the calculator switches to the Katch-McArdle equation, which uses lean body mass instead of sex and age: BMR = 370 + 21.6 × lean mass (kg).
2. Total daily energy expenditure (TDEE). BMR is multiplied by an activity factor: 1.2 if you are sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. The result is roughly how many calories you burn on an average day. The TDEE calculator shows it for every activity level.
3. Your goal. A kilogram of body fat stores roughly 7,700 kcal, or about 3,500 kcal per pound. To lose 0.5 kg (1.1 lb) a week, the calculator takes 7,700 × 0.5 ÷ 7 = 550 kcal a day off your TDEE. To gain, it adds the same way.
4. The macro split. Your calorie target is split by the percentages for your diet type, then turned into grams using the standard energy values: 4 kcal per gram of protein, 4 kcal per gram of carbohydrate and 9 kcal per gram of fat.
Which diet type to choose
| Diet type | Protein / carbs / fat | Good for |
|---|---|---|
| Balanced | 25 / 45 / 30 | General health. Every macro sits inside the ranges the US Institute of Medicine recommends for adults (protein 10–35%, carbs 45–65%, fat 20–35%). |
| High protein | 40 / 30 / 30 | Losing fat while keeping muscle, and staying full on fewer calories. |
| Low carb | 35 / 25 / 40 | People who feel better with fewer carbs and more fat. |
| Keto | 20 / 5 / 75 | A ketogenic diet, which usually means under 50 g of carbs a day. |
| Custom | You choose | Any split, as long as it adds up to 100%. |
There is no single best split for fat loss. When calories and protein are matched, studies comparing low-carb and low-fat diets find similar weight loss. Pick the split you can stick to.
Worked example
A 35-year-old woman, 165 cm (5 ft 5 in) and 70 kg (154 lb), who exercises 3–5 days a week and wants to lose 0.5 kg (1.1 lb) a week on the high-protein split:
- BMR = 10 × 70 + 6.25 × 165 − 5 × 35 − 161 = 1,395 kcal
- TDEE = 1,395 × 1.55 = 2,163 kcal
- Target = 2,163 − 550 = 1,613 kcal a day
- Protein = 40% of 1,613 = 645 kcal ÷ 4 = 161 g
- Carbs = 30% of 1,613 = 484 kcal ÷ 4 = 121 g
- Fat = 30% of 1,613 = 484 kcal ÷ 9 = 54 g
That is 2.3 g of protein per kg of body weight, which is in the range that helps protect muscle in a calorie deficit. Spread over 4 meals, it works out at about 40 g of protein, 30 g of carbs and 13 g of fat per meal.
Macros at common calorie targets
Grams per day for each diet type, at three calorie levels. Find the row closest to your target.
| Calories | Diet (P/C/F %) | Protein | Carbs | Fat |
|---|---|---|---|---|
| 1,500 | Balanced (25/45/30) | 94 g | 169 g | 50 g |
| High protein (40/30/30) | 150 g | 113 g | 50 g | |
| Low carb (35/25/40) | 131 g | 94 g | 67 g | |
| Keto (20/5/75) | 75 g | 19 g | 125 g | |
| 2,000 | Balanced (25/45/30) | 125 g | 225 g | 67 g |
| High protein (40/30/30) | 200 g | 150 g | 67 g | |
| Low carb (35/25/40) | 175 g | 125 g | 89 g | |
| Keto (20/5/75) | 100 g | 25 g | 167 g | |
| 2,500 | Balanced (25/45/30) | 156 g | 281 g | 83 g |
| High protein (40/30/30) | 250 g | 188 g | 83 g | |
| Low carb (35/25/40) | 219 g | 156 g | 111 g | |
| Keto (20/5/75) | 125 g | 31 g | 208 g |
How accurate is it?
Any equation is an estimate. Mifflin-St Jeor predicts resting energy expenditure within about 10% of a lab measurement for most healthy adults, but some people sit further from the average. Activity factors add more uncertainty, because “moderately active” covers a lot of different weeks.
Use the result as a starting point:
- Eat at your target for 2–4 weeks and weigh yourself several times a week under the same conditions.
- Compare the average change with what you expected. If you are losing slower than planned, take off 100–200 kcal a day, mostly from carbs or fat. If faster, add the same back.
- Recalculate after every 5 kg (10 lb) of change, because a lighter body burns less.
Safety checks
The calculator warns you if your target falls below 1,200 kcal a day for women or 1,500 kcal for men, the usual minimums without medical supervision, and if your goal means losing more than 1% of your body weight a week. Faster loss tends to cost more muscle and is harder to keep up. The calculator is designed for healthy adults. It is not suitable during pregnancy or breastfeeding, for anyone under 18, or for anyone with a history of eating disorders.
Frequently asked questions
How do I calculate my macros?
Start with your calorie target. Estimate your BMR with the Mifflin-St Jeor equation, multiply it by an activity factor between 1.2 and 1.9 to get your TDEE, then add or subtract calories for your goal. Split that number into percentages for protein, carbs and fat, and divide by 4 kcal per gram for protein and carbs and 9 kcal per gram for fat. The calculator above does all of this as you type.
What should my macros be to lose weight?
Calories decide whether you lose weight. Macros mostly decide what that weight is made of. Most people do well with a deficit of 250 to 550 kcal a day and protein at about 1.6 to 2.2 g per kg of body weight (0.7 to 1 g per lb), which helps keep muscle while you lose fat. The high-protein preset (40% protein, 30% carbs, 30% fat) gets most people into that range.
Is 40/30/30 a good macro split?
40/30/30 means 40% of calories from protein, 30% from carbs and 30% from fat. It is a popular split for cutting because the extra protein helps you keep muscle and stay full. It is not magic. If you prefer more carbs for training, a balanced split works just as well as long as your calories and protein are right.
How many grams of protein should I eat a day?
The minimum for adults (the RDA) is 0.8 g per kg of body weight. People who lift weights gain the most muscle at about 1.6 g per kg, with an upper range of 2.2 g per kg (Morton et al., 2018). When dieting, 1.8 to 2.7 g per kg helps protect muscle. Use the protein calculator for a figure based on your goal and age.
Should I count macros or calories?
Calories set the direction of your weight. Macros make sure you get enough protein and a mix of carbs and fat you can stick to. If tracking everything feels like too much, track calories and protein only. That covers most of the benefit.
Why does the calculator ask for body fat percentage?
It is optional. If you enter it, the calculator uses the Katch-McArdle equation, which works from lean body mass. That can be more accurate for very muscular people or people carrying a lot of body fat, as long as your body fat estimate is reasonable. If you leave it blank, it uses Mifflin-St Jeor.
How often should I recalculate my macros?
Recalculate every 4 to 6 weeks, or after every 5 kg (10 lb) of change. As you lose weight you burn fewer calories, so the same intake produces slower loss over time.
Are macros different for men and women?
The method is the same. The Mifflin-St Jeor equation gives men about 166 kcal a day more than women of the same weight, height and age, and the safe minimum intake is higher for men (1,500 kcal) than for women (1,200 kcal). The macro percentages do not change by sex.