Subtraction in the numbers dashboard widget

Hi there, I’m wanting to move my budgeting out of excel and into Monday.com. Currently I already use forms to create invoicing data for my accounts team so it would be helpful to keep it all in the platform so I don’t have to duplicate. However, without the ability to subtract in the numbers widget it’s impossible for me to see remaining funds.

Use case:
My projects are all sponsored and that makes my budget. I have 1 board with 2 groups, one for incoming invoices (ie. my incoming and available spend) and another for invoices paid (ie. my expenses). I’d like to use the number widget in the dashboard to subtract the paid invoices from the sponsorship to see how much money I have left to spend.

We can already get a sum, is there any way that we can get a subtract or does anyone have a workaround I can use?

Thanks,
Sam