We estimate the number counts of line emitters at high redshift and their evolution with cosmic time based on a combination of photometry and spectroscopy. We predict the H$alpha$, H$beta$, [OII], and [OIII] line fluxes for more than $35,000$ galaxies down to stellar masses of $sim10^9$ $M_{odot}$ in the COSMOS and GOODS-S fields, applying standard