I need to specify date variables for a Crystal Report date range parameter. The UI only allows literal date values when setting up the parameters. Am I missing something or is this by design?

Choose "DateVariableField" for data type
"RangeValue" for Range Type.
Then you will have 2 fields to enter variable dates.

Example 1st of last month, last of last month:
{DATEADD(Months|{DATEFORMAT(yyyy-MM-01)}|yyyy-MM-dd|-1|yyyy-MM-dd)}
{DATEADD(Days|{DATEFORMAT(yyyy-MM-01)}|yyyy-MM-dd|-1|yyyy-MM-dd)}

Obviously I was missing something. Works perfectly. Thanks.