Maybe this isn’t what you’re after, but Monday does have a built-in feature for deadlines that shows when items are overdue. See this article for more info.
Feel free to share a screenshot of the formula and your board and I’d be happy to take a look. You’ve most likely made a syntax error when implementing the formula.
Hiya, I use a timeline column, date column plus some formula columns.
The date column has an automation to set the completed date to the day the status changes to done.
The first formula column shows if the task was completed early or late.
IF({Completed Date}=“”,“N/A”,DAYS({Timeline#End},{Completed Date}))
The second formula column tells me if the task is pending/overdue or if it was completed on time or late.
IF({Timeline}=“”,“Pending”,If({Status}=“Done”,If({Completed Early/Late}<0,“Done Overdue”,“Done On Time”),If(DAYS(TODAY(),{Timeline#End})<0,“Pending”,If(rounddown(DAYS(TODAY(),{Timeline#End}),0)=0,“Due Today”,“Overdue”))))
I’m pretty sure I got all this from a help article but can’t find it now sorry!