To calculate macros, find basal metabolic rate (BMR) with the Mifflin-St Jeor equation, multiply it by an activity factor to get total daily energy expenditure (TDEE), adjust for a goal, then split the calorie target among protein, carbohydrate and fat and convert to grams at 4 kcal/g for protein and carbs and 9 kcal/g for fat.
What are macros?
Macronutrients, or "macros," are the three nutrients that supply most dietary energy: protein, carbohydrate and fat. Each provides a fixed number of calories per gram, known as the Atwater factors:
| Macronutrient | Calories per gram |
|---|---|
| Protein | 4 kcal |
| Carbohydrate | 4 kcal |
| Fat | 9 kcal |
Alcohol supplies about 7 kcal per gram but is not counted as a macro. Because fat holds more than twice the energy of the other two, a small number of grams of fat accounts for a large share of calories.
Step 1: How do you calculate BMR?
BMR is the energy the body uses at complete rest. The Mifflin-St Jeor equation (Mifflin et al., 1990) is the most widely used estimate. With weight in kilograms, height in centimeters and age in years:
- Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5
- Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161
To convert units: pounds ÷ 2.2046 = kilograms, and inches × 2.54 = centimeters.
Step 2: How do you find TDEE?
TDEE adds the energy spent on daily movement and exercise. It is estimated by multiplying BMR by an activity factor. These multipliers are conventional rules of thumb rather than measured values:
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | 1.2 |
| Lightly active | Light exercise 1–3 days a week | 1.375 |
| Moderately active | Moderate exercise 3–5 days a week | 1.55 |
| Active | Hard exercise 6–7 days a week | 1.725 |
| Very active | Hard daily exercise plus a physical job | 1.9 |
Most people overestimate their activity level. Choosing one level lower and adjusting after a few weeks of tracking is a common, practical approach.
Step 3: How do you set a calorie target?
Adjust TDEE for the goal:
- Maintain weight: eat at TDEE.
- Lose weight: subtract a moderate amount; 250–500 kcal a day below TDEE is a common starting range.
- Gain weight or muscle: add 250–500 kcal a day.
The adjustment is an estimate. Body weight trends over two to four weeks show whether the target needs to move up or down.
Step 4: How do you choose a macro split?
A macro split assigns a percentage of calories to each nutrient. The National Academies (formerly the Institute of Medicine) set Acceptable Macronutrient Distribution Ranges (AMDRs) for adults, ranges associated with adequate nutrient intake and reduced chronic disease risk:
| Macronutrient | Adult AMDR (% of calories) |
|---|---|
| Protein | 10–35% |
| Carbohydrate | 45–65% |
| Fat | 20–35% |
Popular diet styles often sit partly outside these ranges. A typical "balanced" fitness split of 30% protein, 35% carbohydrate and 35% fat has carbohydrate below the AMDR, and ketogenic diets (around 70% fat and 5% carbohydrate) are far outside it. Such diets are a personal choice, but they are not what the AMDRs describe.
Check protein in grams per kilogram
Percentages alone can give odd protein amounts at very low or very high calorie intakes, so it helps to check protein against body weight. The adult Recommended Dietary Allowance (RDA) is 0.8 g of protein per kilogram of body weight per day. The RDA is the amount that meets the needs of nearly all healthy adults, not a ceiling; people who train hard or are losing weight often eat more.
Step 5: How do you convert percentages to grams?
For each macro:
grams = (calorie target × percentage) ÷ calories per gram
Divide by 4 for protein and carbohydrate and by 9 for fat.
Worked example: calculating macros from start to finish
A 35-year-old woman, 70 kg (154 lb), 165 cm (5 ft 5 in), moderately active, wants to lose weight gradually.
1. BMR (Mifflin-St Jeor, women): 10 × 70 + 6.25 × 165 − 5 × 35 − 161 = 700 + 1,031.25 − 175 − 161 = 1,395 kcal/day
2. TDEE: 1,395.25 × 1.55 = 2,163 kcal/day
3. Calorie target: 2,163 − 500 = 1,663, rounded to 1,660 kcal/day
4. Macro split: 30% protein, 40% carbohydrate, 30% fat (all three inside the AMDRs).
5. Grams:
| Macro | Calories | Calculation | Grams per day |
|---|---|---|---|
| Protein | 30% × 1,660 = 498 kcal | 498 ÷ 4 | 124.5 g (about 125 g) |
| Carbohydrate | 40% × 1,660 = 664 kcal | 664 ÷ 4 | 166 g |
| Fat | 30% × 1,660 = 498 kcal | 498 ÷ 9 | 55.3 g (about 55 g) |
Check: 125 × 4 + 166 × 4 + 55 × 9 = 500 + 664 + 495 = 1,659 kcal, which matches the target after rounding.
Protein check: 124.5 g ÷ 70 kg = about 1.8 g/kg, well above the RDA of 0.8 g/kg (56 g for her weight) and a level often chosen to help preserve muscle while in a calorie deficit.
How accurate is a macro calculation?
Every step is an estimate. Mifflin-St Jeor predicts the average BMR for people of a given size and age, and individuals can differ noticeably from it. Activity multipliers are broad categories, and food labels and tracking apps carry their own rounding. Treat the first result as a starting point:
- Track intake and body weight for two to four weeks.
- If weight is not moving in the intended direction, change calories by 100–200 kcal a day.
- Keep protein steady and adjust carbohydrate and fat to fit the new total.
Common mistakes when counting macros
- Using percentages without checking grams. Very low calorie targets can leave protein too low even at 30%.
- Ignoring cooking oils, sauces and drinks. These are mostly fat or sugar and add up quickly.
- Mixing raw and cooked weights. Meat loses water when cooked, so 100 g cooked contains more protein than 100 g raw.
- Recalculating too rarely. BMR and TDEE fall as body weight drops.
This guide is educational and is not medical or dietary advice; people with health conditions should consult a doctor or registered dietitian.