The structural integrity of engineering components is crucial in engineering design, because they are prone to damage due to repeated loading and unloading, particularly under low-cycle fatigue (LCF) conditions. This study presents a critical strain-based phase-field damage model (PFDM) for ductile fatigue. The model captures the accumulation of damage by relating the critical strain energy to fracture energy release rate. The PFDM formulation is integrated into Finite Element Method (FEM) software, enabling the simulation of damage phenomena under cyclic loading. The model considers the evolution of damage driven by energy-based criteria. A numerical example demonstrates the capability of the approach to predict fatigue-induced failure and validates the model’s functionality. This work underscores the importance of energy-based damage indicators for modeling fatigue in ductile materials and a possibility to use critical total strain energy as a material parameter.