User Inputs that are used in Calculation fields

[JenDean]

I’m trying to create a Dashboard that pulls the SPEND of ad platforms and places them into a Looker dashboard.  I would then like the user to input a BUDGET of each platform and have the dashboard spit out a calculation of what % of the spend was used against the budget (SPEND / BUDGET)%

Is there a way to have a user input a number that is then used dynamically as a calculation field? 

Furthermore if I could save that BUDGET user input and only have it be replaced when we update the dashboard with the next user input that would be amazing.