  In this paper we revisit and update the computation of thermal corrections to
the stability of the electroweak vacuum in the Standard Model. At zero
temperature, we make use of the full two-loop effective potential, improved by
three-loop beta functions with two-loop matching conditions. At finite
temperature, we include one-loop thermal corrections together with resummation
of daisy diagrams. We solve numerically---both at zero and finite
temperature---the bounce equation, thus providing an accurate description of
the thermal tunneling. Assuming a maximum temperature in the early Universe of
the order of $10^{18}$ GeV, we find that at finite temperature the instability
bound excludes values of the top mass $M_t \gtrsim 173.6$ GeV, with $M_h \simeq
125$ GeV and including uncertainties on the strong coupling. We discuss the
validity and temperature-dependence of this bound in the early Universe, with a
special focus on the reheating phase after inflation.
