User1724605321 posted
Hi bangbonvilla,
Welcome to ASP.NET Forum .
When you want to add calculated page totals to a Header or Footer , for example, a per-page sum total if the page includes numeric values. Because you cannot reference the fields directly, the expression that you put in the header or footer must
reference the name of the report item (for example, a text box) rather than the data field:
=Sum(ReportItems!Textbox1.Value)
Please refer to below article for details :
https://msdn.microsoft.com/en-us/library/dd220421.aspx
https://msdn.microsoft.com/en-us/library/dd255256.aspx
Best Regards,
Nan Yu