Celoxis allows you to bill the time-entries and expenses spent on your project.
On every project you can decide if your project follows a Fixed price or Hourly based billing. To set this value, edit your project and click on the Advanced tab and navigate to the Financials section, you can select the project's billing model. Only the time-entries of "Hourly" billing model are automatically marked as billable. The billing rates can be entered at project or company level.
The billing amount of a task is calculated as:
Actual Revenue of a task = Actual Billable Hours + Approved and Billable expenses.
The Bill rate (Time code or User) is used to calculate the Actual Billable Hours.