We reconsider the issue of the number of e-foldings before the end of
inflation at which observable perturbations were generated. We determine a
plausible upper limit on that number for the standard cosmology which is around
60, with the expectation that the actual value will be up to 10 below this. We
also note a special property of the λϕ4 model which reduces the
uncertainties in that case and favours a higher value, giving a fairly definite
prediction of 64 e-foldings for that model. We note an extreme (and highly
implausible) situation where the number of e-foldings can be even higher,
possibly up to 100, and discuss the shortcomings of quantifying inflation by
e-foldings rather than by the change in aH. Finally, we discuss the impact of
non-standard evolution between the end of inflation and the present, showing
that again the expected number of e-foldings can be modified, and in some cases
significantly increased.Comment: 7 pages RevTeX4 file with one figure incorporated. Minor updates to
match version accepted by Physical Review