Line 18 is only for the cost of health insurance for those who are not officers or >2% shareholders. Insurance paid for those individuals goes on line 7 or line 8. See the instructions for Lines 7 and 8 of Form 1120-S and see chapter 6 of IRS Pub. 535. The S-corp gets a deduction for wages paid, reports the taxable wages on your W-2 and, as I explained above, a >2% shareholder takes the deduction on their individual tax return, line 17 of Schedule 1 (Form 1040). The result is that FICA must be paid on the amount paid for the health insurance of >2% shareholders.
