I've create a dummy data to evaluate the result. If you've similar data as per the sample attached below then find my approach,
Create few calculated fields
Current Day Sales which is 7/10/2018 : 125
Previous Day Sales which is 7/9/2018 : 115
So, growth %: (125-115)/115 is 8.7%
(SUM([Current Day Sales])-SUM([Previous Day Sales]))/SUM([Previous Day Sales])
If you drag these fields on canvas then you'll have this view
Now, to get the final output as per requirement, you just need to put these calculated fields on label like this and edit the label as per attachment
Let us know if this help else share some sample mock up data in packaged workbook/excel.
Workbook v10.5 attached for your reference.
Sample v10.5.twbx 19.3 KB
I was sure I could do this with a text field. The big question is: can you do this with the matrix/tabular graph? Is it possible to have this listed in the cell? I would assume not without first doing the transformation to the data before it gets loaded into Tableau?
Sounds doable Glen.
It'll be helpful for us to give you any solution, if you share some sample mock up data either in packaged workbook or in excel with your expected output.