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We study inflation in Weyl gravity. The original Weyl quadratic gravity,based on Weyl conformal geometry, is a theory invariant under Weyl symmetry of(gauged) local scale transformations. In this theory Planck scale ($M$) emergesas the scale where this symmetry is broken spontaneously by a geometricStueckelberg mechanism, to Einstein-Proca action for the Weyl "photon" (of massnear $M$). With this action as a "low energy" broken phase of Weyl gravity,century-old criticisms of the latter (due to non-metricity) are avoided. Inthis context, inflation with field values above $M$ is natural, since this isjust a phase transition scale from Weyl gravity (geometry) to Einstein gravity(Riemannian geometry), where the massive Weyl photon decouples. We show thatinflation in Weyl gravity coupled to a scalar field has results close to thosein Starobinsky model (recovered for vanishing non-minimal coupling), with amildly smaller tensor-to-scalar ratio ($r$). Weyl gravity predicts a specific,narrow range $0.00257 \leq r\leq 0.00303$, for a spectral index $n_s$ withinexperimental bounds at $68\%$CL and e-folds number $N=60$. This range of valueswill soon be reached by CMB experiments and provides a test of Weyl gravity.Unlike in the Starobinsky model, the prediction for $(r, n_s)$ is not affectedby unknown higher dimensional curvature operators (suppressed by some largemass scale) since these are forbidden by the Weyl gauge symmetry.

Weyl $R^2$ inflation with an emergent Planck scale