Reference: Moore, Thomas A., A General Relativity Workbook, University Science Books (2013) – Chapter 16; Problem P16.6.
We can get an expression for the mass of a black hole as a function of time, taking into account its evaporation through radiation. The total lifetime of the black hole of initial mass is given by
From the equation we derived earlier (eqn. 11 in this post, with variables renamed to match what we’re doing here), the mass at time is
A plot of versus looks like this:
The rate of mass loss increases towards the end of the black hole’s life.