Individuals: File 2012 Form 1040, 1040A, or 1040EZ. For automatic 6-month extension file Form 4868 and deposit estimated tax. Pay the first installment of 2013 estimated tax.
Household Employers: File Schedule H with Form 1040 if you paid $1,700 or more to a household employee.
Partnerships: File 2012 Form 1065 and furnish a copy of Sch. K-1 to each partner.
Electing Large Partnerships: File 2012 Form 1065 calendar year return.
Corporations: Deposit the first installment of your estimated tax for 2013.
Employers: Deposit payroll tax for March if the monthly deposit rule applies.