  We investigate all single-field, slow-roll inflationary models whose
slow-roll parameters scale as 1/N in the limit of a large number of e-folds N.
We proof that all such models belong to two universality classes, characterised
by a single parameter. One class contains small field models like hilltop
inflation, while the other class consists of large field models like chaotic
inflation. We give the leading expressions for the spectral index and
tensor-to-scalar ratio r, which are universal for each class, plus subleading
corrections for a number of models. This predicts r either to be unobservably
small, r<0.01, or close to the present observational limit, r~0.07.
