Billing rates for time entered in can be defined within a project, task or user level. This can be configured within each client or project.
To do so, go to Settings > Company Settings > Project & Clients. Then select the EDIT link next to the project or client you wish to configure. Select in the Default Billing Type drop-down, to calculate the billable rates based on the user’s default rate, the projects default rate, or the task’s default rate.
When a project is selected, the billable rate will now be calculated based on the default billable type.