I'd join the data source to itself. Take for example the attached Excel sample. It has two columns, Year and Net Fee. Join them together using a join calculation as shown below. Make sure the join is a left join so that you do not drop the first year, which will not have a prior year match.
This will result in 4 fields -- Year and Net Fee of current year and Year and Net Fee for prior year.
From there, you can just do some simple math to get the difference, etc. It's made much simpler because both current and prior year data are now on a single row.
See attached Excel sample and Tableau workbook.
If this solves your problem, please be sure to mark this answer as correct. Thanks!