Deduction for a Plan that Calculates Based on Number of Dependents

If a plan has deductions based on the number of dependents such as: 

Medical Insurance:

 

EE Only                 $20.00

EE Spouse            $16.00  Additional

EE Child                $ 4.00    Additional

 

So if John Q Public is Employee,  Spouse,  + 2 Children deduction would be:

 

$20.00 + $16.00 + $4.00 +$4.00  = $44.00

 

I know you can set it up as:

 

EE Only                $20.00

EE Spouse           $16.00  Additional

EE Child                $ 4.00    Additional

EE Child 2             $8.00    Additional

EE Child 3             $12.00 Additional...

Has anyone set it up based on the numbers of dependents in the dependents file?   We thought about using the national fiscal data but that would include Spouse so it may use an errorneous number.    Setting it up with all the options requires that the employee choose the appropriate number of dependents during open enrollment.  This may cause issues if an employee chooses 1 child when they are actually covering 4.