  I consider the question of possible observability of the total number of
e-folds accumulated during the epoch of inflation. The total number of
observable e-folds has been previously constrained by the de Sitter entropy
after inflation, assuming that the null energy condition (NEC) holds. The NEC
is violated by upward fluctuations of the local Hubble rate, which occur with
high probability in the fluctuation-dominated regime of inflation. These
fluctuations lead at late times to the formation of black holes and thus limit
the observability of inflationary evolution. I compute the maximum number
<Delta N> of e-folds that can be observed in principle through measurements of
the CMB at arbitrarily late times (if the dark energy disappears). The
calculation also provides a reasonably precise definition of the boundary of
the fluctuation-dominated regime, with an uncertainty of a few percent. In
simple models of single-field inflation compatible with current CMB
observations, I find <Delta N> of order 10^5. This upper bound on the
observable e-folds, although model-dependent, is much smaller than the de
Sitter entropy after inflation. The method of calculation can be used in other
models of single-field inflation.
