Track who worked, what they were paid, and what a night actually cleared. Costs only — this is not payroll.
An act's fee is rarely the biggest thing a night costs. Staff and costs is where the rest of it goes, so what a night actually cleared is something you can look at rather than assemble in your head afterwards.
Add the people who work your room — sound engineers, door, security, bartenders, servers, hosts, cleaning, or anything else — then put them on nights.
The night's takings, less what the act cost you — their fee plus whatever they ran up on the house tab — less staff, less the other costs you recorded.
These are event costs only. Rent, utilities and stock sit outside it, so it tells you what a night contributed, not what the business made.
The same inputs answer the other half of the question before the night rather than after it: what it has to take to cover itself. That sits on the date's own page — see break-even and how a show is selling.
If you offer acts food and drink at a discount, set the standing offer once in your booking defaults and record what each act actually ran up. A band on $400 who eats and drinks $180 at the house rate cost you $490, and over a year of Fridays that gap is real money that never appears on paper.