In lattice calculations including isospin-breaking effects, low-energy Standard Model predictions can be unambiguously obtained providing external inputs to define the quark masses, the QCD scale and the value of the electromagnetic coupling. However, there is phenomenological interest to define an isospin-symmetric value of a given observable, or to define the corrections coming from the strong or electromagnetic isospin-breaking effects separately. This separation is known to be prescription-dependent, and a diversity of such prescriptions is used across the lattice community. Since these quantities are actively used, for example in the context of the muon g-2 or radiative corrections to weak decays, the question of quantifying scheme dependency is relevant. In this talk we discuss a general framework to describe these ambiguities, and how to estimate them using lattice data or effective field theories.