The calculation runs properly when data is initially entered but does not auto-refresh when the current date is past the end date of their employment.
In the Storage options for the "Active" Calculation field, do you have the " Do Not Store Calculation Results" box checked off?
The only check box I see in the 'Options for Field "Active"' under calculation is:
"Do not replace existing value for field (if any)" and that is not checked.
My biggest concern is just getting the database to re-run all the calculations for the records.
Change your field to type Calculation instead of using an auto-entered calculation. Then, as rdowler instructed, set it as an unstored calculation.
So this calculation will automatically refresh every time the database is opened?