I need to add a historical date to a report. The date I need is December 31, 2015. The data field I need is "current balance". What date expression would I use?
You've not provided nearly enough information. Relational? Dimensional? How is the date you want to filter on stored in your data source? Is there a time dimension? Or is it an attribute of a table? Member of a dimension?
Are you trying to run a report for the previous year, so that you can run the same report again next year without having to edit it?