  We determine corrections to the Hubble rate due to graviton loops in a
cosmological background spacetime of constant deceleration parameter. The
corrections are gauge-invariant, based on a recent proposal for all-order
gauge-invariant observables in perturbative quantum gravity. We find explicit
expressions for the cases of matter- and radiation-dominated eras and slow-roll
inflation with vanishing second slow-roll parameter. Interestingly, in the
latter case the corrections can be described by a quantum-corrected first
slow-roll parameter, which brings the spacetime closer to de Sitter space.
