You can use ‘Calculated Columns’ in your report, if required.  For instance, you could use a calculated column to show the value of VAT as shown in the example below:

Click on ‘ReportData’

Click on the ‘New Item’ menu and select ‘New Calculated Column’

In the ‘Edit Calculated Column’ modal, enter a ‘Name in Source’, ‘Name’ & ‘Alias’ as required.  Set a ‘Value’ for the field (which could be a calculation of a data field in this example) and the required ‘Type’.

Select ‘OK’ and drag the new calculated field in to your report.