  We investigate the growth of stellar discs in Milky Way-mass galaxies using
the magnetohydrodynamical simulations of the Auriga Project in a full
cosmological context. We focus on the gas accretion process along the discs,
calculating the net, infall and outflow rates as a function of galactocentric
distance, and investigate the relation between them and the star formation
activity. The stellar distributions of around 70% of the simulated galaxies
exhibit an ``inside-out'' pattern, with older (younger) stellar populations
preferentially located in the inner (outer) disc regions. In all cases, we find
a very tight correlation between the infall, outflow and net accretion rates,
as well as between these three quantities and the star formation rate. This is
because the amount of gas which is ultimately available for star formation in
each radial ring depends not only on the infall rates, but also on the amount
of gas leaving the disc in outflows, which directly relates to the local star
formation level. Therefore, any of these rates can be used to identify galaxies
with inside-out growth. For these galaxies, the correlation between the
dominant times of accretion/star formation and disc radius is well fitted by a
linear function. We also find that, when averaged over galaxies with formation
histories similar to the Milky Way, the simulated accretion rates show a
similar evolution (both temporally- and radially-integrated) to the usual
accretion prescriptions used in chemical evolution models, although some major
differences arise at early times and in the inner disc regions.
