Together with our previous studies on membrane fusion and pore nucleation, we complete here another step along the life of the fusion pore by describing its expansion. We have ported the nucleation and expansion processes into two convenient collective variables for the PLUMED 2 development version environment (), easily compilable as an optional module and with source codes freely available on GitHub: . The expansion procedure can be directly used for free energy calculations with any pair of homogeneous/heterogeneous lipid bilayers, at different hydration levels, with or without proteins under the Martini 3 coarse-grained model.