Workflow to populate a field

Hello,

I am looking at the Time records and the ability to report on the "hidden" Rate field. Because of the way the rate field seems to behave on reports (displays $0 if non-billable, and other strange behavior) we are resorting to a workaround.

I've created a new field called "Billing Rate" on the Time record and would like to populate that field with the actual Rate on the entry. (Billing Class rate of the task the employee booked time against).

In some attempts the closest I've gotten is populating this new field with NULL. The rate field is not an option as a "field value" in the workflow so I'm trying to use the formula function {rate}. so "Billing Rate = {rate}" is what is being executed in the workflow. It seems to result in NULL.