Inside-out mass growth of the MW stellar disc. Left: R_birth distribution of stellar mass in different bins of the lookback time (stellar age). Middle: cumulative mass formed at a given R_birth over time. The inner disc (blue lines) exhibits an initial growth with 80% of its mass created by 6–7 Gyr ago, while the outer disc (red lines) formed 80% of its mass <4 Gyr ago. Right: lookback time distribution of stellar mass formation within a 1-kpc-wide radial bin, expressed as a percentage of the total mass formed at the corresponding radius. The symbols show at what lookback time 10 (light blue), 50 (blue), and 90% (dark blue) of mass formed at a given distance from the centre.