Difference Between Fields in Summary Table

I created a summary table of a financial chart with the intention of getting a comparison summary of year end numbers. Because I filter the dates to show year-end financials for both December 2019 and December 2020, the balance is the same and I am finding myself unable to create a formula to see the difference. Is there something I am missing?


Basically, I'd love to add in a column with the differences between 2019 and 2020, and possibly add a second column where I can add comments. 

Thank you for your help.