A theoretical model of dynamic susceptibility and magnetoviscous effect in non-dilute polydisperse ferrofluids with magnetically interacting particles is proposed. This system is considered as homogeneous magnetic colloid of interacting particles, without any heterogenous aggregates. Analysis is based on the mathematically regular approximation of the pair interparticle interaction combined with the effective field method, which leads to very good agreement with the laboratory and computer experiments in the case of dilute ferrofluids with non-interacting particles and with computer simulations of monodisperse ensembles of magnetically interacting ferromagnetic particles. © 2023, The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature.