  In this paper we study the reheating constraints on inflationary models
considering perturbatively decaying inflaton. Important difference with the
existing analysis is the inclusion of explicit decaying dynamics of inflaton
during reheating. One of the important findings of our analysis is the possible
existence of maximum reheating temperature $T_{re}^{max}$ considering
perturbative reheating scenario. For all the models under consideration the
value of this temperature turned out to be $T_{re}^{max} \sim 10^{15}$ GeV.
Corresponding to this value of reheating temperature the duration of reheating
period assumes naturally small value, $N_{re} \simeq 0.3$ which indicates
instantaneous reheating. Most importantly, maximum reheating temperature
$T^{max}_{re}$ also leads to a maximum values of scalar spectral index
$n^{max}_s$ and inflationary e-folding number $N^{max}_{cmb}$ in association
with the observed CMB scale. Based on our general analysis, we have studied
four different inflationary models, and discuss their predictions and
constraints.
