In this contribution, an additive strain model is used to describe the deformation behavior of concrete. The model assumes that elastic, viscous, thermal, and damage-induced strains occur in concrete. The strain components develop independently of each other as a function of the number of load cycles, test duration, and characteristic parameters of the stress cycles. The focus of this paper is on the determination of a creep-relevant stress level to estimate the magnitude of the viscous deformation component as a function of the fatigue stress. Experimentally measured strains of fatigue-loaded concrete specimens are divided into the strain components assumed by the additive strain model and analyzed. The investigations yield new insights into the strain and material behavior of fatigue-loaded concrete.