Clinical studies as well as recent investigations conducted with other methodologies (e.g. neuroimaging, transcranial magnetic stimulation, direct cortical electro-stimulation) leave several unanswered questions about the contribution of the right hemisphere in calculation. All methods increasingly show an involvement of the right hemisphere in functions traditionally believed to be in the domain of the left hemisphere. Novel clinical studies show that right hemisphere acalculia encompasses a wide variety of symptoms, affecting even simple calculation, that cannot be entirely attributed to spatial disorders or to a generic impoverishment of processing resources as previously believed. Moving from the conclusions of these studies, new data will be presented , by means of Direct Cortical Electrostimulation during glioma surgery and Magneto-Encephalography (MEG), concerning simple calculation, i.e., one-digit addition and multiplication. Up to very recent times, these tasks were believed to be carried out by the left hemisphere. The studies reported here show instead how the right hemisphere has its own specific role and that only a bilateral orchestration between the respective functions of each hemisphere guarantees, in fact, precise calculation. The traditional wisdom, that attributes to the right hemisphere a role mostly confined to spatial aspects of calculation, needs to be significantly reshaped. The aim of future studies will be to precisely highlight the nature of the cross-talk between the two hemispheres.