We use the most extensive integral field spectroscopic map of a local galaxy, NGC 628, combined with gas and stellar mass surface density maps, to study the distribution of metals in this galaxy out to 3 effective radii ($Re$). At each galactocentric distance, we compute the metal budget and thus constrain the mass of metals lost. We find that in the disc about 50% of the metals have been lost throughout the lifetime of the galaxy. The fraction of metals lost is higher in the bulge ($\sim$70$\rm \sim 3 \ R_e$).Incontrasttostudiesbasedonthegaskinematics,whichareonlysensitivetoongoingoutflowevents,ourmetalbudgetanalysisenablesustoinfertheaverageoutflowrateduringthegalaxylifetime.Byusingsimplephysicallymotivatedmodelsofchemicalevolutionwecanfittheobservedmetalbudgetatmostradiiwithanaverageoutflowloadingfactoroforderunity,thusclearlydemonstratingtheimportanceofoutflowsintheevolutionofdiscgalaxiesofthismassrange($\rm log(M_\star/M_\odot) \sim 10)$. The observed gas phase metallicity is higher than expected from the metal budget and suggests late-time accretion of enriched gas, likely raining onto the disc from the metal-enriched halo.