Determining your macros comes down to three steps: estimate how many calories you need each day, decide what percentage of those calories should come from protein, fat, and carbohydrates, then convert those percentages into grams. The math is straightforward once you understand what drives each number.
Start With Your Maintenance Calories
Before you can split calories into macros, you need a reasonable estimate of how many calories your body burns in a day. The most widely validated method is the Mifflin-St Jeor equation, which uses your weight in kilograms, height in centimeters, and age in years:
- Men: (9.99 × weight) + (6.25 × height) − (4.92 × age) + 5
- Women: (9.99 × weight) + (6.25 × height) − (4.92 × age) − 161
This gives you your resting energy expenditure, the calories your body burns just keeping you alive. To account for movement and exercise, multiply that number by an activity factor: 1.2 if you’re mostly sedentary, 1.375 for light exercise a few days a week, 1.55 for moderate exercise most days, and 1.725 if you train hard five or six days a week. The result is your estimated maintenance calories.
For example, a 30-year-old woman who weighs 68 kg (about 150 pounds), stands 165 cm (5’5″), and exercises moderately would calculate: (9.99 × 68) + (6.25 × 165) − (4.92 × 30) − 161 = roughly 1,361 calories at rest. Multiplied by 1.55, her estimated maintenance lands around 2,110 calories per day.
If you know your body fat percentage from a DEXA scan or similar measurement, the Katch-McArdle formula can be more precise because it factors in lean body mass directly: 370 + (21.6 × lean mass in kg). This is especially useful if you carry significantly more or less muscle than average for your height and weight.
Adjust Calories for Your Goal
Your maintenance number is a starting point. What you do with it depends on whether you want to lose fat, gain muscle, or stay where you are.
For fat loss, a deficit of 300 to 500 calories below maintenance is a sustainable range that preserves muscle while dropping body fat steadily. For muscle gain, research on resistance-trained individuals suggests a surplus of 5 to 20 percent above maintenance, with more experienced lifters staying at the lower end. That translates to gaining roughly 0.25 to 0.5 percent of your body weight per week, which keeps fat gain minimal. If your maintenance is 2,500 calories, a 10 percent surplus puts you at 2,750.
Set Protein First
Protein is the macro you anchor everything else around because it has the narrowest useful range and the biggest consequences if you get it wrong. It supports muscle repair, immune function, and satiety, and your body can’t store it the way it stores fat or carbohydrates.
The baseline recommendation for a sedentary adult is 0.8 grams per kilogram of body weight per day. That’s the minimum to prevent deficiency, not the amount for optimal body composition. If you lift weights regularly or train for endurance events, the evidence-based range jumps to 1.2 to 1.7 grams per kilogram. Someone weighing 80 kg (176 pounds) who strength trains would aim for roughly 96 to 136 grams of protein daily.
During a calorie deficit, protein needs increase because your body is more likely to break down muscle for energy. Staying at the higher end of that range, around 1.6 to 1.7 grams per kilogram, helps protect lean mass while you lose fat.
Set Fat Next
Dietary fat is essential for absorbing vitamins A, D, E, and K, producing hormones, and protecting heart health. The World Health Organization and Dietary Reference Intakes recommend 20 to 35 percent of total calories from fat. The 20 percent floor exists for a reason: dropping below it can impair absorption of fat-soluble vitamins and essential fatty acids, and low-fat, high-carb diets are associated with unfavorable cholesterol profiles, specifically low HDL and elevated triglycerides.
Most people do well around 25 to 30 percent. If your target is 2,000 calories per day and you choose 25 percent from fat, that’s 500 calories from fat. Since fat contains 9 calories per gram, you divide 500 by 9 to get about 56 grams of fat per day.
Fill the Rest With Carbohydrates
Once protein and fat are set, whatever calories remain go to carbohydrates. This isn’t because carbs are less important. They’re your body’s preferred fuel for high-intensity exercise, brain function, and recovery. It’s simply that protein and fat have firmer minimum thresholds, so carbs become the flexible variable.
Here’s how the final math works. Each gram of protein and each gram of carbohydrate provides 4 calories. Each gram of fat provides 9 calories. Take your total calorie target, subtract the calories assigned to protein and fat, then divide the remainder by 4.
A Complete Example
Take a 35-year-old man who weighs 85 kg (187 pounds), is 178 cm tall (5’10”), lifts weights four days a week, and wants to lose fat slowly.
His resting calories via Mifflin-St Jeor: (9.99 × 85) + (6.25 × 178) − (4.92 × 35) + 5 = roughly 1,787. Multiplied by an activity factor of 1.55, his maintenance estimate is about 2,770 calories. For a moderate deficit, he subtracts 400, targeting 2,370 calories per day.
Protein: at 1.6 grams per kilogram, that’s 136 grams. At 4 calories per gram, protein accounts for 544 calories.
Fat: at 25 percent of total calories, that’s 593 calories. Divided by 9 calories per gram, he gets 66 grams of fat.
Carbohydrates: 2,370 − 544 − 593 = 1,233 remaining calories. Divided by 4, that’s 308 grams of carbs.
His daily macros: 136g protein, 66g fat, 308g carbs.
Why These Numbers Are Starting Points
Every equation is an estimate. Two people with identical stats can have metabolisms that differ by a few hundred calories due to genetics, muscle mass, daily non-exercise movement, and sleep quality. The real calibration happens over two to four weeks of consistent tracking.
Weigh yourself under the same conditions each morning and track the weekly average. If you’re trying to lose fat and the average isn’t trending down after two weeks, reduce your target by 100 to 150 calories, primarily from carbs or fat. If you’re gaining weight faster than expected on a surplus, scale back by the same amount. Protein generally stays fixed unless your body weight changes significantly.
Tracking apps simplify daily logging, but the value is in the weekly trend, not any single day. A day over or under your targets doesn’t matter. What matters is that your weekly averages land close to where you planned. Over time, you’ll develop an intuitive sense of portion sizes and food composition that makes strict tracking optional.
Common Adjustments by Goal
- Fat loss while preserving muscle: Keep protein at 1.6 to 1.7 g/kg, fat at 20 to 25 percent of calories, and fill the rest with carbs. Prioritize protein at each meal to maximize satiety.
- Muscle gain: Use a 5 to 15 percent surplus, protein at 1.4 to 1.6 g/kg, fat at 25 to 30 percent, and the remainder as carbs to fuel training performance.
- General health and maintenance: Protein at 1.0 to 1.2 g/kg, fat at 25 to 35 percent, with carbs making up the balance. This is the most forgiving range because you’re not pushing toward a specific physical outcome.
As your body weight changes, recalculate. Losing or gaining 5 kg shifts your calorie needs enough to warrant plugging your new numbers back into the equation and resetting your macros from there.