Black hole masses from SDSS (Shen et al. 2011) and z > 6 quasars (Bosman et al. 2023; Eilers et al. 2023; Marshall et al. 2023; Yang et al. 2023; Yue et al. 2023), with both Mg II and Balmer line based measurements. The green line shows the one-to-one relation. PJ308-21 is indicated with blue diamonds (NIRSpec and X-shooter data). Overall, the z > 6 quasars show nice agreement between the Mg II and Hβ or Hα-based M_BH, consistent with the ∼0.5 dex scatter of the low-redshift estimates (green region; Vestergaard & Peterson 2006). While a larger sample is needed to confirm these results, these first JWST estimates suggest that the Mg II is a reliable tracer of the black hole mass at both low and high-redshift.