for Example:

you have 10 gm. support, you want to load 15wt% of active component.

make X/(X+10) = 0.15  (X - Actual amount of Active component required finally)

You will get X = ca. 1.7647 gm. of active component needs to be added.

For any catalyst preparation, a certain molarity is intended e.g 0.2mol/dm3; from this, u start to calculate for each mass concentration of each active component and scale down or up to any point.