Time needed for core growth up to 10 M_⊕ at various locations in the disc. The solid black line gives the formation time of the core for pebble accretion in the Hill regime, while grey lines give the time needed to form the critical 10-Earth-mass core by planetesimal accretion. The dashed grey line represents planetesimal fragment accretion from a thin midplane layer, as studied by Rafikov (2004). The red shaded area shows the approximate time interval in which the protoplanetary disc loses its gaseous component and encompasses for example the estimated age of gas giant LkCa 15b (Kraus & Ireland 2012). Core formation needs to occur before this time.