September
Tu 15 Individuals: Pay the third installment of your 2015 estimated tax.
Tu 15 Partnerships: File Form 1065 if you timely requested a 5-month extension.
Tu 15 Corporations: File calendar year Form 1120 or 1120S if you timely requested a 6-month extension.
Tu 15 Corporations: Deposit the third installment of your 2015 estimated tax.
October
Th 15 Individuals: File Form 1040, 1040A, or 1040EZ if you timely requested a 6-month extension.
Th 15 Electing Large Partnerships: File Form 1065-B if you timely requested a 6-month extension.
Th 15 File Form 5500 if you timely requested an extension on Form 5558.
November
Mo 2 File Form 941 for the third quarter.
Mo 2 Deposit FUTA owed through Sep if more than $500.
Tu 10 File Form 941 for the third quarter if you timely deposited all required payments.
December
Tu 15 Corporations: Deposit the fourth installment of your 2015 estimated tax.