Individuals. File a 2017 income tax return. If you want an automatic six-month extension of time to file the return, file Form 4868, “Application for Automatic Extension of Time To File U.S. Individual Income Tax Return.” Then, file Form 1040, 1040A, or 1040EZ by October 15.
If you are not paying your 2018 income tax through withholding (or will not pay in enough tax during the year that way), pay the first installment of your 2018 estimated tax. Use Form 1040-ES.
Employers. For Social Security, Medicare, withheld income tax, and nonpayroll withholding, deposit the tax for payments in March if the monthly rule applies.
Household employers. If you paid cash wages of $2,000 or more in 2017 to a household employee, file Schedule H (Form 1040) with your income tax return and report any household employment taxes. Report any federal unemployment (FUTA) tax on Schedule H if you paid total cash wages of $1,000 or more in any calendar quarter of 2016 or 2017 to household employees. Also, report any income tax you withheld for your household employees.
Corporations. File a 2017 calendar-year income tax return (Form 1120) and pay any tax due. If you want an automatic six-month extension of time to file the return, file Form 7004 and deposit what you estimate you owe.
Corporations. Deposit the first installment of estimated income tax for 2018.