We study F -functions in the context of field theories on S 3 using gaugegravity duality, with the radius of S 3 playing the role of RG scale. We show that the on-shell action, evaluated over a set of holographic RG flow solutions, can be used to define good F -functions, which decrease monotonically along the RG flow from the UV to the IR for a wide range of examples. If the operator perturbing the UV CFT has dimension ∆ > 3/2 these F -functions correspond to an appropriately renormalized free energy. If instead the perturbing operator has dimension ∆ < 3/2 it is the quantum effective potential, i.e. the Legendre transform of the free energy, which gives rise to good F -functions. We check that these observations hold beyond holography for the case of a free fermion on S 3 (∆ = 2) and the free boson on S 3 (∆ = 1), resolving a long-standing problem regarding the non-monotonicity of the free energy for the free massive scalar. We also show that for a particular choice of entangling surface, we can define good F -functions from an entanglement entropy, which coincide with certain F -functions obtained from the on-shell action. Appendix 55 A Perturbative expansion near the maximum of the potential 55 B Calculation of the on-shell action 56 C Calculation of the entanglement entropy 57 -i -D Analytical results for large and small boundary curvature 59 D.1 Large curvature expansion 59 D.2 Small curvature expansion 62 E Holographic entanglement entropy of a spherical region in flat space 68 F De Sitter entanglement entropy and thermodynamics 69 F.1 The de Sitter static patch: thermal entropy, and the ADM mass 69 F.2 Identities from thermodynamic relations 71 G Comments on the renormalization scheme 72 H Zeta-function renormalization vs. covariant counterterms 74 I Further monotonic functions 76 References 78 5 The operator D 3/2 eliminates any dependence on Cct as it only appears in the combination Cct R −3/2 .