Estimated typical time needed for a black hole to grow from a seed mass of M ^seed _BH = 10 ⁶  M _☉ to four different final masses as a function of redshift, assuming a radiative efficiency of _r = 0.1 and the typical Eddington ratio for that mass and redshift bin. The solid line marks the age of the universe as a function of z, the dashed line marks the growth time assuming L/ L _Edd = 1, and the rest of the labeling is the same as that in Figure 5. Although the uncertainties are large, the growth times for SMBHs in Type 1 quasars having M _BH 5 × 10 ⁸  M _☉ are comparable to or greater than the age of the universe, suggesting an earlier phase of accelerated obscured growth. The growth times at z ≲ 0.6 are also longer than the age of the universe, possibly reflecting a shift to fueling by mass loss from evolved stellar populations.