To figure out how much you should eat to gain muscle, you need two numbers: your maintenance calories (the amount that keeps your weight stable) and a surplus of 5 to 20% on top of that. For most people, this works out to roughly 200 to 500 extra calories per day. The exact number depends on your weight, height, age, activity level, and how long you’ve been training.
There’s no single perfect calculator, but the math behind every reliable one is straightforward enough to do yourself. Here’s how to work through it step by step.
Step 1: Estimate Your Maintenance Calories
Your maintenance calories, often called your Total Daily Energy Expenditure (TDEE), combine two things: the energy your body burns at rest and the energy you burn through movement. Start by calculating your Resting Energy Expenditure (REE) using the Mifflin-St Jeor equation, which is the most widely validated formula for people at a healthy weight:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
If you know your body fat percentage (from a DEXA scan or a reliable estimate), the Katch-McArdle formula can be more accurate, especially at higher body fat levels. It scored the highest accuracy rate across body types in a large comparison study. The formula is: 370 + (21.6 × lean body mass in kg). You get your lean mass by subtracting your fat mass from your total weight. For example, if you weigh 80 kg at 20% body fat, your lean mass is 64 kg, giving you a resting expenditure of about 1,752 calories.
Once you have your resting number, multiply it by an activity factor to get your TDEE:
- Lightly active (desk job, training 3 days/week): × 1.375
- Moderately active (some daily movement, training 4–5 days/week): × 1.55
- Very active (physical job or training 6+ days/week): × 1.725
This final number is your estimated maintenance. It’s a starting point, not a perfect measurement. Every formula has a margin of error, which is why tracking your actual weight over the first two weeks matters more than the initial calculation.
Step 2: Add Your Caloric Surplus
A 2023 study in Sports Medicine that directly compared small and large surpluses in trained lifters found that when surpluses exceeded 5 to 15%, the extra calories mostly turned into fat rather than additional muscle. The researchers recommended a surplus of 5 to 20% above maintenance, scaled to training experience: beginners can use the higher end, while more advanced lifters should stay toward the lower end.
In practical terms, that looks like this:
- Beginner (under 1 year of consistent training): 300–500 calories above maintenance, or about 15–20% surplus
- Intermediate (1–3 years): 200–350 calories above maintenance, or about 10–15% surplus
- Advanced (3+ years): 100–250 calories above maintenance, or about 5–10% surplus
The reason for the sliding scale is simple: beginners can add muscle quickly, so their bodies can actually use more of that surplus for growth. Advanced lifters build muscle slowly no matter what, so a large surplus just accelerates fat gain. Aim for a weight gain rate of 0.25 to 0.5% of your body mass per week. For someone weighing 180 pounds (82 kg), that’s roughly 0.45 to 0.9 pounds per week.
A Worked Example
Say you’re a 28-year-old man, 5’10” (178 cm), 170 pounds (77 kg), training four days a week with about two years of experience.
Using Mifflin-St Jeor: (10 × 77) + (6.25 × 178) − (5 × 28) + 5 = 770 + 1,112.5 − 140 + 5 = 1,747.5 calories at rest. Multiply by 1.55 for moderate activity: approximately 2,709 calories for maintenance. As an intermediate lifter, you’d add 10 to 15%, which puts your target at roughly 2,980 to 3,115 calories per day.
How to Split Those Calories: Protein
Protein is the nutrient that directly builds muscle tissue, and the target is well established. The International Society of Sports Nutrition recommends 1.4 to 2.0 grams per kilogram of body weight per day for active people looking to gain muscle. For our 77 kg example, that’s 108 to 154 grams of protein daily. If you’re in a hard training block or dieting down, push toward the higher end.
How you distribute that protein across the day matters. Research in the American Journal of Clinical Nutrition found that each meal needs roughly 3 to 4 grams of leucine, a specific amino acid, to fully activate your body’s muscle-building machinery. That translates to about 25 to 30 grams of protein per meal. Spreading your intake across three to four meals tends to be more effective for muscle growth than loading it all into one or two sittings. At minimum, each protein serving should contain at least 20 grams to meaningfully stimulate muscle building in younger adults.
How to Split Those Calories: Carbs and Fats
After protein, carbohydrates are your primary fuel for resistance training. A joint position statement from the Academy of Nutrition and Dietetics and the American College of Sports Medicine recommends 3 to 5 grams of carbs per kilogram per day for low-intensity or skill-based activity, and 5 to 7 grams per kilogram for moderate programs around an hour a day. Research on experienced lifters suggests a practical range of 3 to 7 grams per kilogram daily for optimizing resistance training performance. For a 77 kg lifter training four days per week, that’s roughly 230 to 540 grams of carbs, with most people landing somewhere around 300 to 400 grams.
Fat fills in the remaining calories after you’ve set protein and carbs. A useful floor is about 0.5 grams of fat per kilogram of body weight, since dietary fat supports hormone production (including testosterone). Most people end up in the range of 0.7 to 1.2 grams per kilogram. Using our example at a 3,000-calorie target with 140 grams of protein and 350 grams of carbs, you’d have about 560 + 1,400 = 1,960 calories accounted for, leaving 1,040 calories for fat, which is roughly 116 grams.
What to Do When the Scale Stalls
Your body doesn’t passively accept a surplus. When you eat more, your non-exercise activity (fidgeting, walking pace, posture changes) often increases unconsciously, burning off some of those extra calories. This is why a calculated surplus doesn’t always produce the expected weight gain.
Weigh yourself daily, first thing in the morning, and use the weekly average to track trends. If your weekly average hasn’t moved after two full weeks, add 100 to 150 calories per day and reassess. If you’re gaining faster than 0.5% of body weight per week, you’re likely accumulating more fat than necessary, and pulling back 100 to 150 calories is reasonable.
This iterative approach is more reliable than any calculator because it accounts for the variables no equation can capture: your genetics, your sleep quality, how much you move outside the gym, and how your metabolism responds to extra food. The formula gives you a starting line. Your scale weight over two to four weeks tells you whether you’ve found the right number.
Quick Reference Cheat Sheet
- Maintenance calories: Mifflin-St Jeor or Katch-McArdle × activity multiplier
- Surplus: 5–20% above maintenance, scaled to experience
- Weight gain rate: 0.25–0.5% of body weight per week
- Protein: 1.4–2.0 g/kg/day, split into 25–30 g servings
- Carbs: 3–7 g/kg/day depending on training volume
- Fat: remaining calories, minimum ~0.5 g/kg/day
- Adjustment pace: add or subtract 100–150 calories every two weeks based on scale trends