The calculation of the mass spectrum is done iteratively in the following way:
Obtaining the running parameters
Everything starts with calculating the running parameters at the scale MZ including the threshold corrections
Afterwards the running parameters the renormalisation scale Q are calculated. These parameters can be given either directly at that scale as input or they are fixed by some GUT conditions and a RGE running is performed. Q itself can be either be a fixed value or can be dynamically chosen. In supersymmetric models, it is common to choose the geometric mean of the stop masses because this usually minimizes the scale dependence of the Higgs mass prediction.
Not all parameters are fixed by the input but some parameters are kept free. These parameters are arranged in a way that all further calculations are done at the minimum of the potential. For this purpose the tadpole equationsTi are solved at tree-level with respect to these free parameters.
As soon as all running parameters are known at the scale Q, they are used to calculate the tree-level mass spectrum.
It is checked if the difference compared to the previously calculated mass spectrum agrees within numerical precision.
If there is no convergence reached, all parameters are evolved to MZ to calculate the changes in the threshold corrections to the SM parameters.
A new iteration is started with the new parameters.
After the parameters have converged, the pole masses are calculated as described here.