We present analytic approximation formulae describing spectral distortions of the Cosmic Microwave Background (CMB) as a function of three basic parameters: the amount of energy injected in the radiation field, the time at which the heating occurred, and the baryon density Omega(b). These formulae allow easy exploitation of the high accuracy measurements of the CMB spectrum to derive constraints on physical processes that may have occurred in the early universe, dispensing with the need of resorting to heavy numerical calculations.
