Logarithmic representation of the difference between output and input stellar mass ℳ_⋆ for spectral fits with fado and starlight (blue and green, respectively) to synthetic spectra corresponding to a) a single-burst star formation scenario approximated by a declining SFR given by exp(− t/τ) with an e-folding timescale τ = 1 Myr and b) continuous star formation at constant SFR. The synthetic input spectra assume solar-metallicity and zero intrinsic extinction, and include the contribution of nebular emission (continuum and lines). The shaded green area around determinations with starlight for the Base SSP library depict ±1σ uncertainties, as obtained from ten fits. A substantial contribution of the reddish nebular continuum to the SED for ages lower than ~10⁷ yr in panel a and lower than ~10⁸ yr in panel b causes the purely stellar fits by starlight to strongly overestimate ℳ_⋆ by up to ~1.8 dex. To the contrary, fado can recover ℳ_⋆ to within less than ~0.5 dex over the entire age interval considered. Results for spectral fits with Base ℱare included in orange for the sake of completeness, but only for models with fado since this base contains 600 elements, twice the maximum number of base elements that starlight can deal with. Note the significant improvement of the results from fado when Base ℱ is used instead of Base , which is due to a better time coverage of evolutionary phases with a strong variation in the LyC photon rate and the Hδ_F absorption Lick index.