Healthcare added to an S Corporate owner\officer does not affect the Net Pay.
It is to increase BOX 1 - Federal Wages on the 941 and W2 forms only. There is no tax benefit - its just compliance.
I suggest on the last pay, add the annual amount paid on the last paycheck or run a payroll adjustment.
This should wash through the expense account used to pay the health insurance, such that you'll see an increase and decrease for the same amount. The decrease is what is reported in Box 14
