As the configurational entropy is a defining characteristic of high entropy alloys, we wish to calculate its value and understand its dependence on temperature and composition. Possible approaches include Monte Carlo simulation, mean field theories and generalized mean field theories of the cluster variation type. All approaches require chemically accurate models for interatomic interactions that can be obtained from first principles total energy calculation. We will compare and contrast entropy estimates based on cluster expansions with alternative approaches utilizing direct first principles molecular dynamics and Monte Carlo simulation. The analysis will focus on refractory alloys based on Ti, V and Cr columns of the periodic table, and the impact of the entropy on alloy stability will be evaluated.