[Lizard]

There is no direct way to insert formulas into fields. However, it is possible to write an AppleScript that would take the value of one (or more) custom data fields for a task, perform some calculation on them, and write the result out as another custom data field for that task. This AppleScript could be designed to do calculations for the currently selected task, or each task in the project. The script can be added to your toolbar, for convenient updating of your file.