I have this exact problem with TurboTax online 2025:
* spouse files as Detroit nonresident (but not me)
* working days allocation is filled out, reducing income earned in city of Detroit
* After e-filing, Form 5121 DOES NOT APPEAR in generated PDF of Michigan/Detroit tax forms
* Workaround mentioned does not work after e-filing on TurboTax online.
* Need Form 5121 to successfully file Detroit taxes by mail
How can I get 2025 Detroit Form 5121?
