To calculate your bulking calories, you need two numbers: your total daily energy expenditure (TDEE) and a surplus of 5 to 10 percent on top of it. For most people, this works out to roughly 200 to 500 extra calories per day, depending on body size and activity level. The math involves three steps: estimating your resting metabolic rate, adjusting for activity, then adding the surplus.
Step 1: Estimate Your Resting Metabolic Rate
Your resting metabolic rate (RMR) is the number of calories your body burns doing absolutely nothing, just keeping your organs running and your temperature stable. The most widely recommended formula for estimating it is the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics considers the most accurate for most adults.
For men: (9.99 × weight in kg) + (6.25 × height in cm) − (4.92 × age in years) + 5
For women: (9.99 × weight in kg) + (6.25 × height in cm) − (4.92 × age in years) − 161
To convert your weight, divide pounds by 2.2. To convert your height, multiply inches by 2.54. As a quick example, a 28-year-old man who weighs 180 pounds (81.8 kg) and stands 5’10” (177.8 cm) would get: (9.99 × 81.8) + (6.25 × 177.8) − (4.92 × 28) + 5 = about 1,790 calories at rest.
Step 2: Adjust for Activity Level
Your RMR only reflects what your body burns at complete rest. To get your TDEE, you multiply it by an activity factor that accounts for your training and daily movement. The standard multipliers are:
- Sedentary (desk job, no exercise): RMR × 1.2
- Lightly active (light exercise 1 to 3 days per week): RMR × 1.375
- Moderately active (moderate exercise 3 to 5 days per week): RMR × 1.55
- Very active (hard training 6 to 7 days per week): RMR × 1.725
- Extremely active (intense training plus a physical job): RMR × 1.9
Most people who lift weights three or four days a week and have an otherwise sedentary job fall somewhere between lightly active and moderately active. If you’re unsure, lean toward the lower multiplier. It’s easier to add calories later than to cut back after gaining too much fat. Using the example above, our 180-pound lifter training four days per week would multiply 1,790 by 1.55 to get a TDEE of roughly 2,775 calories.
Step 3: Add Your Caloric Surplus
Once you have your TDEE, add 5 to 10 percent. A smaller surplus (5 percent) is better if you tend to gain fat easily or want a leaner bulk. A larger surplus (10 percent) suits people who are naturally lean, train at high volume, or have struggled to gain weight in the past.
For our example lifter at 2,775 calories, a 5 percent surplus adds about 140 calories (bringing the total to roughly 2,915), while a 10 percent surplus adds about 278 calories (bringing the total to roughly 3,050). Most people will land somewhere in the range of 200 to 500 extra calories per day. Going much higher than that doesn’t accelerate muscle growth. It just speeds up fat gain.
How Fast You Should Gain Weight
A good target is no more than one pound of body weight per week. If you’re consistently gaining faster than that, the extra weight is almost certainly fat rather than muscle. For most natural lifters, half a pound per week is a more realistic pace that keeps the bulk relatively lean.
Weigh yourself at the same time each day, ideally first thing in the morning, and track the weekly average rather than any single reading. Daily weight fluctuates by one to three pounds based on water, sodium, and food volume. If your weekly average stays flat for two weeks straight, bump your intake up by 100 to 150 calories. If it’s climbing faster than a pound per week, scale back by the same amount.
Where Those Calories Should Come From
Protein is the priority. A reliable target for muscle growth is 0.7 grams per pound of body weight per day. A 180-pound person would aim for about 126 grams of protein daily. If you’re carrying extra body fat and trying to stay leaner during your bulk, going up to 0.8 to 1 gram per pound can help preserve the muscle-to-fat ratio of your gains.
For the rest of your calories, general dietary guidelines suggest 45 to 65 percent of total intake from carbohydrates and 20 to 35 percent from fat. During a bulk, carbohydrates deserve the higher end of that range because they fuel training performance and help replenish the energy stored in your muscles between sessions. Fats should stay at a minimum of about 20 percent of total calories, since dropping below that can interfere with hormone production.
As a practical split for bulking, aim for roughly 25 to 30 percent of calories from protein, 45 to 55 percent from carbohydrates, and 20 to 30 percent from fat. These are starting points. Adjust based on how you feel in training, how your weight is trending, and your food preferences.
A Full Calculation Example
Here’s the complete process for a 25-year-old woman who weighs 140 pounds (63.6 kg), stands 5’6″ (167.6 cm), and lifts weights four days per week.
RMR: (9.99 × 63.6) + (6.25 × 167.6) − (4.92 × 25) − 161 = approximately 1,370 calories.
TDEE: 1,370 × 1.55 (moderately active) = approximately 2,125 calories.
Bulking calories at a 10 percent surplus: 2,125 + 213 = approximately 2,340 calories per day.
Protein target at 0.7 grams per pound: about 98 grams (392 calories from protein). That leaves roughly 1,950 calories to split between carbohydrates and fat. At 50 percent carbohydrates from total calories, she’d eat about 293 grams of carbs. At 25 percent fat, she’d eat about 65 grams of fat.
Why Calculators Are Starting Points, Not Answers
Every formula, including Mifflin-St Jeor, estimates your metabolic rate with a margin of error. Two people with identical height, weight, age, and training schedules can have metabolic rates that differ by several hundred calories due to genetics, muscle mass, sleep quality, and daily non-exercise movement like fidgeting and walking around.
Treat your calculated number as a two-week experiment. Eat at that level consistently, track your morning weight, and see what happens. If you’re gaining at the right pace (roughly half a pound to one pound per week), you’ve found your number. If not, adjust by 100 to 200 calories and run another two-week check. This feedback loop matters more than any formula, because it’s based on what your body actually does rather than what an equation predicts.