The SuperNEMO experiment aims to test the Majorana nature of neutrinos, looking for the neutrinoless double beta decay. The final detector's goal is to reach a sensitivity of $10^{26}$ years on the $^{82}$Se $0\nu\beta\beta$ decay half-life. The SuperNEMO demonstrator is under construction with $6.23$ kg of $^{82}$Se. Decay electrons are tracked in a wire chamber, and their energies measured calorimetrically. The calorimeter is composed of $712$ optical modules: plastic scintillators, mainly coupled with $8''$ photomultipliers. It achieves $8$% FWHM energy and $400$ ps time resolution, at $1$ MeV. Calorimeter commissioning began in $2019$. The calorimeter's energy response was calibrated using the internal $^{208}$Tl spectrum, and photomultipliers' gains were equalised at $1$ MeV. A Cobalt-$60$ source, emitting two coincident gammas, was used to determine time resolution. The demonstrator's calorimeter performance is presented.