Do you mean compound or running total?
(I think of compund as being where they were paid $500 in Jan, and if they hit their target in Feb, they get a $500 bonus for feb in addition to a matching bonus for all months prior)
I didn’t build it out, but assuming it is a just a running total
Have a ‘Hit-Target’ table with 2 fields Text ‘months’ and Linked Field ‘Employees’
When an employee hits their target for a month, add them to that month.
Back in another table with the employees, where there is now a ‘Target-Hit’ field, use a $500*Count() on that field.