Determining your macros is a three-step process: estimate how many calories you burn, decide how those calories should split between protein, carbs, and fat based on your goal, then convert those percentages into grams. The whole calculation takes about five minutes once you understand the logic behind it.
Step 1: Estimate Your Daily Calories
Before you can split calories into macros, you need to know roughly how many calories your body uses in a day. That starts with your basal metabolic rate (BMR), the energy your body burns just to keep you alive at rest. The most widely used formula is the Mifflin-St Jeor equation:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
If you think in pounds and inches, multiply your weight in pounds by 0.45 to get kilograms, and your height in inches by 2.54 to get centimeters. For a 35-year-old woman who weighs 150 pounds (68 kg) and stands 5’6″ (168 cm), the math looks like this: (10 × 68) + (6.25 × 168) − (5 × 35) − 161 = 1,394 calories at rest.
But you don’t lie in bed all day, so you multiply your BMR by an activity factor to get your total daily energy expenditure (TDEE):
- Sedentary (desk job, little exercise): BMR × 1.2
- Lightly active (exercise 1–3 days/week): BMR × 1.375
- Moderately active (exercise 3–5 days/week): BMR × 1.55
- Very active (hard exercise 6–7 days/week): BMR × 1.725
Using the same example with moderate activity: 1,394 × 1.55 = roughly 2,161 calories per day. That’s your maintenance number, the calorie level where your weight stays stable. Everything else builds from here.
Step 2: Adjust Calories for Your Goal
Your maintenance calories only stay the same if your goal is to maintain your current weight. If you want to lose fat or gain muscle, you adjust up or down.
For fat loss, a deficit of about 500 calories per day typically produces a loss of half a pound to one pound per week. That’s considered a sustainable pace that doesn’t tank your energy or trigger excessive muscle loss. So if your maintenance is 2,161 calories, you’d aim for around 1,660.
For muscle gain, a surplus of 5 to 20% above maintenance supports growth while limiting unnecessary fat gain. On a 2,161-calorie maintenance, that’s roughly 100 to 430 extra calories per day. Starting at the lower end (around 5 to 10%) is smart. You can always increase if you’re not seeing progress after a few weeks, but it’s harder to undo excess fat gain later.
Step 3: Set Your Macro Ratios
Now you divide those total calories among the three macronutrients. Each one provides a different amount of energy per gram: protein has 4 calories per gram, carbohydrates have 4 calories per gram, and fat has 9 calories per gram. The federal Dietary Guidelines set broad acceptable ranges for adults: 10 to 35% of calories from protein, 45 to 65% from carbs, and 20 to 35% from fat. But where you land within those ranges depends on what you’re trying to accomplish.
Protein
Protein is the macro most people should set first, because it matters most for preserving muscle during a cut and building it during a surplus. The baseline recommendation is 0.8 grams per kilogram of body weight (about 0.36 grams per pound), but that’s the minimum to avoid deficiency, not an optimal target for someone who exercises. Most active people do better with 1.2 to 2.0 grams per kilogram, depending on training intensity. If you lift weights regularly and want to build or preserve muscle, aiming for the higher end of that range makes sense.
Protein also has a practical advantage for fat loss: your body burns 15 to 30% of protein’s calories just digesting it, compared to 5 to 10% for carbs and 0 to 3% for fat. A higher protein intake slightly boosts your metabolic rate and keeps you fuller between meals.
Fat
Fat supports hormone production, brain function, and the absorption of certain vitamins. Going below about 20% of total calories for extended periods can interfere with these processes. Most people do well setting fat at 25 to 30% of calories. If you find that higher-fat meals keep you more satisfied, pushing toward 35% and pulling carbs down slightly is a reasonable adjustment.
Carbohydrates
Whatever calories remain after protein and fat are accounted for go to carbohydrates. Carbs are your body’s preferred fuel for high-intensity exercise, so people who train hard generally benefit from keeping them at 45% or above. If you’re more sedentary, you can let them drift toward the lower end of that range.
Turning Percentages Into Grams
Here’s where the numbers come together. Say your adjusted calorie target is 1,660 (fat loss) and you choose a 30% protein, 35% carb, 35% fat split.
- Protein: 1,660 × 0.30 = 498 calories ÷ 4 = 125 grams
- Carbs: 1,660 × 0.35 = 581 calories ÷ 4 = 145 grams
- Fat: 1,660 × 0.35 = 581 calories ÷ 9 = 65 grams
Those gram targets are what you’d actually track in a food logging app. You don’t need to hit them exactly every day. Staying within 5 to 10 grams on protein and fat, and being in the right ballpark on carbs, is precise enough to see results over weeks.
Common Starting Points by Goal
If the math feels overwhelming, these starting ratios work well for most people and can be fine-tuned later:
- Fat loss: 30% protein, 35% carbs, 35% fat. The higher protein ratio helps preserve muscle and manage hunger in a deficit.
- Muscle gain: 25% protein, 50% carbs, 25% fat. Extra carbs fuel training and support recovery when you’re in a surplus.
- General health or maintenance: 20–25% protein, 45–50% carbs, 25–30% fat. This sits comfortably within the federal guidelines and works for moderately active people.
These are starting points, not prescriptions. Someone doing two-a-day training sessions needs more carbs. Someone who feels sluggish on higher carbs and more alert with higher fat can adjust. The “right” macros are the ones that support your energy, your training, and your ability to stick with the plan consistently.
Why Your Macros Will Change Over Time
The numbers you calculate today aren’t permanent. As your weight changes, your BMR changes with it. Losing 15 pounds means your body burns fewer calories at rest, which means your maintenance drops and your macros shift. The same is true in reverse if you gain muscle. Recalculating every 10 to 15 pounds of change, or every couple of months, keeps your targets aligned with your actual body.
Activity level matters too. A week where you’re stuck at a desk for 12 hours a day and skip the gym doesn’t demand the same carbohydrate intake as a week where you train five times. Some people adjust daily, others use a weekly average. Either approach works as long as you’re paying attention to trends rather than obsessing over single-day numbers.
The most common mistake is setting macros once and never revisiting them. Your body adapts. If fat loss stalls for more than two or three weeks, you likely need to either reduce your calorie target by another 100 to 200 calories (pulling from carbs or fat, not protein) or increase your activity. If you’re trying to gain muscle and the scale isn’t budging, bump your surplus up by 100 calories and reassess in two weeks.