  We discuss how to calculate non-equilibrium universal amplitude ratios in the
functional renormalization group approach, extending its applicability. In
particular, we focus on the critical relaxation of the Ising model with
non-conserved dynamics (model A) and calculate the universal amplitude ratio
associated with the fluctuation-dissipation ratio of the order parameter,
considering a critical quench from a high-temperature initial condition. Our
predictions turn out to be in good agreement with previous perturbative
renormalization-group calculations and Monte Carlo simulations.
