Calculating a calorie surplus comes down to three steps: estimate how many calories your body burns in a day, then eat a set amount above that number. Most people aiming to gain muscle should eat 10–20% more than their daily maintenance calories, which typically works out to an extra 200–500 calories per day depending on body size and activity level. Here’s how to find your specific number.
Step 1: Estimate Your Basal Metabolic Rate
Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest, just to keep your organs running, your lungs breathing, and your cells functioning. It accounts for the largest chunk of your daily calorie burn, usually 60–70% of the total.
The most widely recommended formula is the Mifflin-St Jeor equation. The American Dietetic Association found it was more likely to predict resting metabolic rate within ±10% of measured values than competing formulas. Here’s how it works:
- 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 use pounds and inches, convert first: divide your weight in pounds by 2.2 for kilograms, and multiply your height in inches by 2.54 for centimeters. For example, a 30-year-old man who weighs 180 pounds (81.8 kg) and stands 5’10” (177.8 cm) would calculate: (10 × 81.8) + (6.25 × 177.8) – (5 × 30) + 5 = 1,782 calories per day at rest.
Step 2: Factor In Your Activity Level
Your BMR only reflects rest. To get your total daily energy expenditure (TDEE), the actual number of calories you burn in a full day, multiply your BMR by an activity factor:
- Sedentary (desk job, little or no exercise): BMR × 1.2
- Lightly active (light exercise 1–3 days per week): BMR × 1.375
- Moderately active (moderate exercise 3–5 days per week): BMR × 1.55
- Very active (hard exercise 6–7 days per week): BMR × 1.725
- Extremely active (intense training plus a physical job): BMR × 1.9
Using the example above, if that 30-year-old man lifts weights four days a week and walks regularly, the “moderately active” multiplier gives him a TDEE of roughly 2,762 calories per day (1,782 × 1.55). That’s his maintenance level, the intake where his weight stays roughly stable.
Be honest with yourself about which category fits. Most people overestimate their activity. If you work out three or four times a week but sit at a desk the rest of the day, “lightly active” or “moderately active” is usually more accurate than “very active.”
Step 3: Add Your Surplus
Now add 10–20% on top of your TDEE. That percentage range comes from sports nutrition guidelines and is designed to produce a weight gain of about 0.25–0.5% of your body weight per week, slow enough to favor muscle over fat.
For the example above, a 10% surplus on a 2,762-calorie TDEE means eating about 2,038 extra calories, totaling roughly 3,038 per day. A 20% surplus would land around 3,314. The difference between those two numbers matters more than it looks. Over a month, the higher end adds roughly 4,000 more calories, which could mean more fat gain if your training isn’t demanding enough to use those extra calories for muscle.
Where to Start in That Range
If you’re relatively new to weight training (less than six months of consistent lifting), aim for the higher end, closer to 20%. Beginners build muscle faster and can put those extra calories to work more efficiently. If you have several years of training experience, stick closer to 10%. Experienced lifters gain muscle more slowly, so a large surplus mostly ends up stored as fat.
In concrete numbers, most people land somewhere between 250 and 500 extra calories per day. A smaller person eating 2,000 calories at maintenance might add 200–400. A larger, very active person at 3,200 maintenance might add 320–640.
How to Split Those Calories Across Macronutrients
A calorie surplus builds muscle only if the raw materials are there, especially protein. Sports nutrition experts generally agree on 1.6–2.2 grams of protein per kilogram of body weight per day to maximize muscle growth. For a 180-pound (81.8 kg) person, that’s roughly 131–180 grams of protein daily. Spacing it out into doses of 20–40 grams every three to four hours appears to stimulate muscle building more effectively than loading it all into one or two meals.
Carbohydrates fuel your training sessions and recovery. Active individuals typically need 5–8 grams per kilogram of body weight per day, though the upper end of that range is reserved for people training at high intensities for 12 or more hours a week. For most recreational lifters, moderate carbohydrate intake fills glycogen stores without overshooting.
Fat should make up the remainder of your calories. There’s no need to go extremely low-fat during a surplus. Dietary fat supports hormone production and absorbs certain vitamins. A practical split for many people in a surplus looks like 25–35% of total calories from fat, with protein and carbs filling the rest.
Why Your Calculated Number Is a Starting Point
Every formula is an estimate. The Mifflin-St Jeor equation is the most accurate widely available tool, but even it can be off by 10% in either direction. Your actual metabolism is shaped by genetics, muscle mass, sleep quality, stress, and other factors no equation can capture.
Your body also burns calories just digesting food, a process called the thermic effect. Protein costs the most to digest, using 15–30% of its calories during processing. Carbohydrates use 5–10%, and fats only 0–3%. This means a high-protein diet effectively leaves fewer “net” calories available than the same calorie count from a high-fat diet. It’s one reason high-protein surpluses tend to produce leaner gains.
The practical takeaway: use your calculated surplus as a two-week experiment. Weigh yourself under consistent conditions (same time of day, same clothing, after using the bathroom) and track the weekly average. If you’re gaining 0.25–0.5% of your body weight per week, your surplus is in the right zone. If the scale isn’t moving, add 100–200 calories. If you’re gaining faster than 0.5% per week, you’re likely adding more fat than necessary, so trim back by 100–200 calories.
Adjustments for Women
Women generally need a smaller absolute surplus because they carry less total muscle mass and have lower baseline calorie needs. The same 10–20% guideline applies, but the resulting number is usually lower since the starting TDEE is lower.
Hormonal cycles also play a role. During the luteal phase (the roughly two weeks before a period), progesterone rises and increases protein breakdown, which may mean slightly higher protein needs during that window. At the same time, estrogen promotes fat burning and spares muscle protein, so women tend to use more fat and less carbohydrate for fuel during exercise compared to men. Some women find they perform better and feel less fatigued when they increase carbohydrate intake slightly during the luteal phase to compensate for shifts in how their body uses fuel.
These differences don’t change the core math of a surplus, but they do mean that women may benefit from cycling their carbohydrate and protein intake across their menstrual cycle rather than keeping macros perfectly static every day.
A Quick-Reference Calculation
Putting it all together for a practical example: a 25-year-old woman who weighs 140 pounds (63.6 kg), stands 5’6″ (167.6 cm), and lifts weights three days a week:
- BMR: (10 × 63.6) + (6.25 × 167.6) – (5 × 25) – 161 = 1,360 calories
- TDEE: 1,360 × 1.375 (lightly active) = 1,870 calories
- 10% surplus: 1,870 + 187 = roughly 2,057 calories per day
- 20% surplus: 1,870 + 374 = roughly 2,244 calories per day
- Protein target: 1.6–2.2 g/kg = 102–140 grams per day
She would start at the lower or middle end of that surplus range, track her weight for two weeks, and adjust based on the rate of gain. The entire process is iterative. The calculation gets you close, and consistent tracking dials it in.