The residual contribution in COSMO-type activity coefficient models rely on a transcendental equation called the “self-consistency” equation, normally solved by a simple successive substitution method. In our previous work, a classical Newton-Raphson method was tested in order to solve this set of equations. Contradicting the usual experience, it was found that Newton method becomes slower than successive substitution when the number of COSMO segments increases. Nevertheless, in the present work we used the resulting converged Jacobian matrix from Newton method to compute COSMO-based models' exact derivatives, with respect to any independent variable, by means of the implicit function theorem. The proposed method was tested for model's derivatives with respect to temperature and number of mols, against numerical derivative calculations. Also, the derivatives of COSMO-SAC with respect to the number of mols were inferred by the Gibbs-Duhem consistency test.