Employers. Ask employees whose withholding allowances will be different in 2019 to fill out a new Form W-4 or Form W-4(SP). The 2019 revision of Form W-4 will be available by mid-December at www.IRS.gov/FormW4.
Employers. For Social Security, Medicare, and withheld income tax, file Form 941 for the third quarter of 2018. This due date applies only if you deposited the tax for the quarter in full and on time.
Employers. For Social Security, Medicare, withheld income tax, and nonpayroll withholding, deposit the tax for payments in October if the monthly rule applies.