A calorie surplus exists when, over a certain period, usually viewed over a day or a week, more energy is taken in than used. The surplus energy is available to the body in addition, for example for building muscle mass, but also for storing body fat, depending on how large the surplus is and how training is designed. The counterpart is the calorie deficit, in which less energy is taken in than used.
In practice, a moderate calorie surplus is often used deliberately to give the body enough building material and energy for muscle building. A very large surplus does not usually lead to proportionally more muscle growth, but mainly to a greater gain in body fat.
Relevance for training and nutrition
For targeted muscle building, a calorie surplus is often combined with a suitable training plan; you can find details in the guide training plan for muscle building. An adequate protein intake is important here, so that the additional energy surplus benefits mainly muscle building and not just fat gain. How large a sensible surplus is depends heavily on individual factors and can only be given as a rough guide.
