* File Form 941 for the second quarter if you timely deposited all required payments.
September 17
* Corporations: File calendar year Form 1120S if you timely requested a 6-month extension.
*Partnerships: File calendar year Form 1065 if you timely requested a 6-month extension.
*Individuals: Pay the third installment of your 2018 estimated tax - Use Form 1040-ES.