The acquisition of isothermal remanent magnetization (IRM) curves through the application of stepwise-increasing uniaxial fields to a rock-magnetic sample provides an important non-destructive tool for the investigation of coercivity spectra (Dunlop & Özdemir 1997). We show that, through the use of an automated procedure based on the expectation–maximization algorithm (Dempster et al. 1977), both saturated and non-saturated IRM acquisition curves can be effectively modelled into their individual coercivity contributions.