- September 15 –
- Third quarter installment of 2017 individual and corporation estimated income tax is due.
- S corporations: Filing deadline for 2016 tax returns for S corporations that requested/received a six-month extension.
- Partnerships: Filing deadline for 2016 tax returns for partnerships that requested/received an automatic six-month extension.
- Electing large partnerships: Filing deadline for 2016 tax returns for electing large partnerships that requested/received a six-month extension.
- October 16 – Filing deadline for 2016 individual or corporation tax returns that requested/received a six-month extension. Pay taxes due by this date.
