Theory Driven Evolution of the Weak Mixing Angle

We present the first purely theoretical calculation of the weak mixing angle in the MS scheme at low energies by combining results from lattice QCD with perturbation theory. We discuss its correlation with the hadronic contribution to the anomalous magnetic moment of the muon and to the energy dependence of the electromagnetic coupling. We also compare the results with calculations using cross-section data as input. Implications for the Standard Model prediction of the mass of the W boson are also discussed.