The observed matter-antimatter asymmetry of the universe is an outstanding mystery of physics that cannot be explained within the Standard Model. Many beyond the Standard Model (BSM) explanations have been proposed, and experimental data is needed to constrain the wide space of BSM models. Neutron-antineutron oscillations are predicted to be a signature of some BSM baryogenesis models and can be cleanly probed by low-energy experiments. Connecting experimental data on neutron-antineutron transition rates to fundamental BSM theory parameters requires QCD matrix elements of six-quark operators effectively parameterizing BSM physics at low energies. I will discuss work to calculate neutron-antineutron transition matrix elements using lattice QCD and the renormalization group. I will highlight how these QCD results can be used to reliably assess the reach of current and future neutron-antineutron experiments into BSM parameter space.