Unable to change the tax year dates from calendar to fiscal

[USAOzi]

Why can I NOT override the calendar year dates for Form10409/1040SR so that it reflects a fiscal year that begins July 1 20xx and ends June 30 20xx?

The option to change shows at the top of the Form 1040/1040SR but the override option to allow me to change the default January 1 to December 31 is greyed out and can't be used.

WHY?

How do I get this to work?

[tagteam]

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.

[dmertz]

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.