November 1, 2025, 4:59 pm | Read time: 4 minutes
The term bulking phase is often used by some amateur bodybuilders as an excuse for a few extra pounds. But what does it really mean? And how high should calorie intake be during the bulking phase to keep fat gain as low as possible? Prof. Dr. Stephan Geisler explains.
More Calories for More Muscle Mass
As the name suggests, the bulking phase (also known as the bulking phase) is about building more body mass. The term comes from the professional bodybuilding scene and has referred for many decades to the practice of increasing food intake during the off-season to build more body mass. But how does it actually work, and what should you pay attention to?
Biologically, this behavior is easy to explain: If you want to build more muscle mass, you should consume more calories than the body needs just to maintain its organ functions and the so-called thermogenesis (the body’s “heating system”).
Strict Diet and Muscle Mountains–Why This Combo Doesn’t Work
Because: Why should the body build muscles when it is in a caloric deficit (a kind of mini-famine)? More muscle mass would only mean more organic mass–and thus require a higher calorie intake. In the body’s survival function, this would naturally make no sense. So, let go of the idea of doing a “strict diet” while simultaneously building enormous muscle mountains.
According to various studies, this is possible to a limited extent, but most studies only dealt with minimal calorie deficits and more or less untrained subjects.
Bulking Phase Without Fat Gain–Correct Calculation of Calories
When talking about mass, muscle mass is, of course, meant, but unfortunately, it doesn’t always work so well, and a few pounds of fat often sneak in during the bulking phase. To avoid this or at least keep fat gain as low as possible, it’s advisable not to go overboard. This means: Get a rough overview of how many calories your body really needs at complete rest (basal metabolic rate) and then add a bit more.
Various formulas are suitable for estimating your basal metabolic rate. You can find an overview of different formulas here. The Harris-Benedict formula, for example, integrates weight, height, age, and gender.
Estimating Basal Metabolic Rate with the Harris-Benedict Formula
Women
- Basal metabolic rate [kcal/24 h] = 655.0955 + (9.5634 x weight in kilograms) + (1.8496 x height in centimeters) – (4.6756 x age in years)
Men
- Basal metabolic rate [kcal/24 h] = 66.4730 + (13.7516 x weight in kilograms) + (5.0033 x height in centimeters) – (6.7550 x age in years)
Basal Metabolic Rate Plus 500 Calories–And You’re in the Bulking Phase
Please remember that the value you calculate is only the basal metabolic rate. That is, the amount of energy your body needs to survive without any exertion. Then add physical activity. You could either measure this with tracking systems or simply calculate it using the so-called PAL value (PAL = Physical Activity Level). Here you can find a table to determine your own PAL.
If you want to be on the safe side, add about 500 calories, and you’re in the bulking phase.
How to Reduce Body Fat Without Losing Muscle
“I Recommend This Training to My Clients When They Want to Lose Weight”
After the Bulking Phase Comes the Cutting Phase
In the cutting phase, you go the opposite way. You slightly reduce calorie intake below the required amount (about 300 to 500 calories) and try to shed excess fat to reveal the newly gained muscles. You essentially redefine your body.
What to Consider in Training?
Theoretically, you can also tailor your training to the different phases, but this has not been scientifically studied, and everyone preaches something different here. My recommendation: During the bulking phase, also do “light endurance training” to keep fat burning alive, and during the cutting phase, don’t train too often or too long to avoid the risk of losing muscle mass in a too-strong calorie deficit.