September
- Monday, September 17 Corporations: File calendar year Form 1120S if you timely requested a 6-month extension.
- Monday, September 17 Partnerships: File calendar year Form 1065 if you timely requested a 6-month extension.
- Monday, September 17 Individuals: Pay the third installment of your 2018 estimated tax – Use Form 1040-ES.
- Monday, September 17 Corporations: Deposit the third installment of your 2018 estimated tax.
- Monday, September 17 Electing Large Partnerships: File Form 1065-B if you timely requested a 6-month extension.
October
- Monday, October 15 Individuals: File Form 1040, 1040A, or 1040EZ if you timely requested a 6-month extension.
- Monday, October 15 Corporations: File calendar year Form 1120 if you timely requested a 6-month extension.
- Wednesday, October 31 File Form 941 for the third quarter.
- Wednesday, October 31 Deposit FUTA owed through Sep if more than $500.
November
- Tuesday, November 13 File Form 941 for the third quarter if you timely deposited all required payments.
December
- Monday, December 17 Corporations: Deposit the fourth installment of your 2018 estimated tax.
