15 Oct October 31
Employers: For Social Security, Medicare, and withheld income tax, file IRS Form 941 for the third quarter of 2018. Deposit any undeposited tax under the accuracy of deposit rules. (If your tax liability is less than $2,500, you can pay it in full with a timely filed return). If you deposited the tax for the quarter in full and on time, you have until November 13 to file the return.
For federal unemployment tax, deposit the tax owed through September if more than $500.