  GM2Calc is a leading tool for calculating precise contributions to $a_\mu$ in
the Minimal Supersymmetric Standard Model. In this proceeding we detail GM2Calc
version 2 where it is extended so it can calculate two-loop contributions to
$a_\mu$ in the Two-Higgs Doublet Model (2HDM), based on the work in Ref. [1].
The 2HDM is a simple model, yet it is one of the few single field extensions of
the Standard Model which is able to explain the muon $g-2$ anomaly. We
demonstrate the powerful and flexible 2HDM capabilities of GM2Calc2, which
include the most precise contributions in the literature and allow the user to
work in their favourite type of the 2HDM as well as use complex and lepton
flavour violating couplings. With its multiple interfaces and input
flexibility, GM2Calc2 is a powerful tool both as a standalone code and as part
of a larger code toolchain.
