Im getting an invalid formula error but am not sure why.

Test the subtraction in another formula. If that doesn't work then that is your problem. Without testing it myself this is my best guess. If the math doesn't work then it's a type error and you will need to use a sql function to convert. Wherever you get stuck try breaking the problem down into pieces and going from there. Useful strategy for all kinds of troubleshooting.

@pen one : If you use Formula(Text) _CASE WHEN {custbody104} is NULL THEN TO_CHAR(ROUND({today}-{trandate})) ELSE {custbody104} END_ If you use Formula(Numeric) _CASE WHEN {custbody104} is NULL THEN TO_NUMBER(ROUND({today}-{trandate})) ELSE {custbody104} END_ You can use NVL function rather than CASE statement _NVL({custbody104}, TO_NUMBER(ROUND({today}-{trandate})))_