The irreversibility of quantum channels is directly linked to both exact quantum error correction and the data-processing inequality, and plays a key role in quantum information theory. In this work, we introduce a quantifier for irreversibility of quantum channels using normalized dual maps, which we call the dual-map infidelity, and we also reinterpret the optimal infidelity and the near-optimal infidelity as two irreversibility quantifiers. We show that all these three quantifiers satisfy the basic properties required of an irreversibility quantifier, and share the same maximum and minimum values. The dual-map infidelity is optimization-free, and has lower computational complexity than the near-optimal infidelity, as it avoids the matrix square roots and matrix inversion required by the near-optimal infidelity. We also establish two-sided bounds relating the dual-map infidelity to the optimal infidelity. We further obtain a necessary and sufficient condition under which the normalized dual map of a quantum channel coincides with the celebrated Petz recovery map. Finally, to demonstrate the utility of the dual-map infidelity as a performance metric for quantum error correction codes, we evaluate it for several qubit codes and the thermodynamic code and compare its behavior with that of the other two quantifiers.