It might be best to solve this with a separate sheet rather than in the grand total line (or better yet, use a separate worksheet as a grand total). A table calculation cannot be computed based on Table (Down) and also asked to run a separate computation specific for the Totals line; as such, it can represent to the total across the Categories in each month (which will always represent 100% for totals) or asked to do a % of total across the months. Creating a separate sheet may allow you to redefine the Table Calculations: Addressing and Partitioning for the view that represents the monthly totals.
Separate sheet I can not do because similar type of sheets we have 15 so I need so many sheets , it is not affordable for my workbook. Thanks
If any other way please let me know.