A new filter method known as Savitzky–Golay allows the reduction of reactivity fluctuations. The filter reduces fluctuations that are found in the nuclear power signal does not attenuate to the reactivity value. The method can be applied with a time step of up to T = 0.01 s and a noise level of up to σ = 0.1. This formulation employs a Gram polynomial approximation of degree d = 2, to calculate the convolution coefficients by means of an analytic formula that is implemented computationally and avoids ill-conditioning issues caused by the inversion of a linear system. The results show better values in the maximum difference and the mean absolute errors of reactivity in comparison with the results reported in the literature.