When you are consuming calories at a surplus level, you are at a positive energy balance. This means more energy is consumed than expended.
Three things happen when in a surplus:
1. Your body will store the excess energy. Depending on the type of surplus you are in, it will store it as either fat or lean muscle tissue, resulting in an increase in body mass.
2. As your body adapts to the excess energy, it will want to increase energy expenditure. Your BMR and NEAT will naturally both go up and you may find you feel like exercising for longer or with a higher intensity.
3. You will feel great. When in a healthy and balanced energy surplus, you will have more energy, your quality of sleep will be better and your body will be able to manage stress and recover at a faster rate.