We provide for primes p≥5 a method to compute valuations appearing in the “formal” Katz expansion of the family [Formula presented] derived from the family of Eisenstein series E_κ^⁎. We will describe two algorithms: the first one to compute the Katz expansion of an overconvergent modular form and the second one, which uses the first algorithm, to compute valuations appearing in the “formal” Katz expansion. Based on data obtained using these algorithms we make a precise conjecture about a constant appearing in the overconvergence rates related to the classical Eisenstein series at level p. The study of these overconvergence rates of the members of this family goes back to a conjecture of Coleman.