It sounds like you’re looking for this feature?
These are the comments from Monzo’s Head of Design on the idea.
https://community.monzo.com/t/total-spent-per-day-1/2643/6?u=alexs
Hugo has said that he’s planning to enable users to see this information but not in the feed itself -
https://community.monzo.com/t/display-running-balance-with-each-entry/6832/22?u=alexs
I hope that helps!