The Euclid and WFIRST cosmological missions will observe many millions of H-alpha emission line galaxies and so in preparation for these missions it is crucial that we understand the properties of these galaxies. I will present results from two projects that focused on (i) examining the number density of H-alpha emitting galaxies, and (ii) examining how H-alpha emitters populate cosmic structures (a property referred to as the ‘bias’). In both instances we use a galaxy formation model to simulate a Euclid-like survey and a WFIRST-like survey. Our predicted number densities for H-alpha emitters are consistent with the WISP survey and the empirical models presented by Pozzetti et al. (2016), though with a reduced scatter. We find that for both the Euclid-like and the WFIRST-like survey, the linear bias of H-alpha emitters evolves according to b(z) = 0.7z + 0.7, which is consistent within error with existing bias measurements from HiZELS.