  The effective potential is a widely used phenomenological tool to investigate
phase transitions occurring in the early Universe at finite temperature. In the
standard perturbative treatment the potential becomes complex in some region of
the background field values due to the non-convex nature of the classical
potential in models with spontaneous symmetry breaking. The imaginary part
renders the minimization of the potential impossible when at finite temperature
the absolute minimum is in the complex region. In this talk we introduce a
simple method to calculate an effective potential that is fully real based on
the optimized perturbation theory scheme. We apply the method for models that
extend the Standard Model with an additional singlet scalar.
