Anything is possible if the Artist and their Manager agree it in writing;
however the norm is 20% of everything the artist earns. Occasionally, a Manager
may demand 25% but this is usually reserved to situations where the Manager has
more work to do, such as so-called "manufactured" bands (like boybands or
girlbands created through auditions). Likewise it may also be as low as 15% or
even 10%, particularly in the case of Songwriter or Producer managers.
They would typically be paid commission for the duration of their contract which
may be a multi-year term. In the event of a Manager being fired by the Artist,
the Manager is usually entitled to continue earning commission for a set period,
sometimes at a reduced rate (ie 10%).