Unable to change the tax year dates from calendar to fiscal

You establish a tax year when you file your first return using that tax year.

 

If you want to change your tax year, you need to file Form 1128.

 

Most individual taxpayers use a calendar year and, likely, TurboTax is programmed for calendar-year taxpayers.

 

You may have to print your return and change the dates manually.

The TurboTax help for the fiscal-year date field explicitly states that TurboTax does not support the preparation of fiscal-year tax returns and that all calculations are performed on a calendar-year basis.