The Tax Department is streamlining withholding tax and wage reporting forms and Web File applications. Complete Form W-4 so that your employer can withhold the correct federal income tax from your pay.Give Form W-4 to your employer. (See Section III.) A completed Form K-4 (42A804), Kentucky's Withholding Certificate, must be on file for each employee. Notice: Some internet browsers have a built in PDF viewer that may not be compatible with our forms. You must complete a new W4 within 10 days from the day you anticipate you will incur an Iowa income tax liability for the calendar year.