Simple calculations in contact properties

We’re a nonprofit. We have two different custom contact properties, one that shows the total donation amount users made in our old donation platform, and one that shows total donation amount in the new platform. We want to be able to provide a monthly impact/donation summary to users that sums these two amounts.

It would be great if workflows and contact properities could do a simple calculation like this instead of me having to manually export + run the numbers in Excel + reimport every time.