Variable Goals

I am attempting to build sales goals into a dashboard. The issue is that my goals table does not have any unique values that can be tied to another table. 

Sales Rep|Month(as the date of the 1st of the month)|Daily Goal

Each month the goal is adjusted based on the previous month if needed. This means that the goal table must have a goal for every rep for every month (each rep has 12 lines on the table). Any suggestions how to get this into a column or a measure on my dashboard that will relate to my other data?