  Within the framework of self-force theory, we compute the gravitational-wave
energy flux through second order in the mass ratio for compact binaries in
quasicircular orbits. Our results are consistent with post-Newtonian
calculations in the weak field and they agree remarkably well with
numerical-relativity simulations of comparable-mass binaries in the strong
field. We also find good agreement for binaries with a spinning secondary or a
slowly spinning primary. Our results are key for accurately modelling
extreme-mass-ratio inspirals and will be useful in modelling
intermediate-mass-ratio systems.
