The stability regions for CBO and CFO agree with the reported experimental and theoretical results. Furthermore, we have calculated surface energy values for different terminations of the (100), (110), (001) facets of CBO and (110), (111), (100), (001), and (012) facets of CFO. The surface energy values were compared in ternary surface phase diagrams, including the calculated stability region of the bulk phases of CFO and CBO. The stoichiometrically terminated (001) and (012) surfaces of CBO and CFO, respectively, are the surfaces with the lowest formation energy within the stability region. Cu-deficient surfaces are favored compared to Fe-deficient surfaces in CFO. In CBO, the Cu-deficiency is preferred as well.