How to Determine Your Best Macros for Weight Gain and Loss

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Whether you’re trying to pack on muscle or drop body fat quickly, the math is the same: calories determine the scale, macros determine what the scale is measuring. Two people can eat the same number of calories and get completely different body composition results depending on where those calories come from .

Here’s the breakdown based on your age, body weight, and goal.

Step 1: Calculate Your TDEE

Your Total Daily Energy Expenditure (TDEE) is the number of calories your body burns in a day. Everything else is built on this number .

TDEE = BMR × Activity Factor

Your Basal Metabolic Rate (BMR) is the calories your body burns just keeping you alive — breathing, heartbeat, cell repair. Age, weight, height, and sex all factor in .

The Mifflin-St Jeor equation is the most widely used formula :

For men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5

For women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161

Activity factors:

Sedentary (desk job, little exercise): BMR × 1.2
Lightly active (on your feet sometimes): BMR × 1.375
Moderately active (exercise 3–5 days/week): BMR × 1.55
Very active (physically demanding job or daily training): BMR × 1.725
Extremely active (heavy daily training): BMR × 1.9

Step 2: Adjust Calories for Your Goal

Your TDEE is your maintenance number. To gain or lose weight, you need to adjust from there :

For weight loss: Subtract 300–500 calories per day from your TDEE for moderate fat loss
For weight gain: Add 200–300 calories per day to your TDEE for lean muscle gain

To lose weight quickly: A deficit of 20–25% below TDEE is generally considered safe for more rapid fat loss while preserving muscle — provided protein stays high .

To gain weight quickly: A surplus of 10–20% above TDEE is optimal . Going much beyond 300 calories above TDEE does not accelerate muscle growth — it mainly adds body fat .

Step 3: Set Your Protein First

Protein is the most important macro for body composition. It builds muscle, preserves lean mass during a calorie deficit, and keeps you fuller longer .

The standard recommendation: 0.7–1 gram of protein per pound of body weight .

For weight loss: Aim for the higher end of the range (0.9–1 gram per pound) since preserving muscle becomes harder in a calorie deficit
For weight gain: 0.7–1 gram per pound covers muscle growth needs
If you’re carrying significant excess body fat: Use your goal body weight or lean body mass instead of current weight

If you weigh 180 pounds and are in a deficit, aim for 160–180 grams of protein per day.

Step 4: Set Your Fat, Then Fill with Carbs

Fat is essential for hormone production, joint health, and absorbing vitamins. It has a physiological floor that carbs do not .

Fat: Set at 25–30% of total daily calories . Going below 20% consistently can impair hormone production, particularly testosterone and estrogen .

To convert fat percentage to grams: (total calories × fat percentage) ÷ 9 (since fat has 9 calories per gram)

Carbohydrates: Fill the remaining calories . Carbs are your body’s preferred fuel source, especially for training .

To convert remaining calories to carbs: remaining calories ÷ 4 (since carbs have 4 calories per gram)

Quick Reference: Macros by Goal

For Weight Loss (2,000-calorie example):

Protein: 0.9–1g per pound body weight
Fat: 25% of calories (≈55g)
Carbs: remaining calories (≈200–225g)

For Weight Gain (2,800-calorie example):

Protein: 0.7–1g per pound body weight
Fat: 25–30% of calories (≈78–93g)
Carbs: remaining calories (≈325–375g)

Why Age Matters

Age affects BMR directly. As you get older, your BMR declines — muscle mass naturally decreases and hormonal shifts slow metabolic rate. The Mifflin-St Jeor equation accounts for this by subtracting 5 calories per year of age for men and 5 calories per year for women .

Practical takeaway: Older adults often need slightly fewer calories and may benefit from protein at the higher end of the range to preserve muscle mass.

The Bottom Line

The formula is simple:

Calculate your TDEE using your age, weight, height, and activity level
Adjust calories — subtract 300–500 for loss, add 200–300 for gain
Set protein first — 0.7–1g per pound of body weight
Set fat — 25–30% of total calories
Fill the rest with carbs

As with any calculator, treat the output as a starting point. Track your intake and body weight for 2–3 weeks and adjust based on real-world results . The calculator gets you in the right range. Consistent tracking dials it in.

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This article was written with AI.