My residence with husband is in Minnesota. As of mid-2023, I am now considered an employee of Missouri. In mid-2023, HR started taking state taxes for Minnesota and Missouri. I physically worked in Missouri for three days since the conversion to a Missouri employee as I work remotely. My husband is retired, and only has income from joint investments. I will complete the Missouri non-resident form to file with my taxes and will file a joint Federal return for all income. How is joint investment income determined when I file the married filing separately state taxes? I suspect I will only file a married filing separately Missouri tax return as my husband does not have Missouri earned income. Is that correct? Will my husband and I file separately for the Minnesota return, splitting out the investment income? I will use Turbo Tax and purchase a second state return. Thanks for any responses.
Missouri can tax only the income you earned on the three days you physically worked in Missouri. The income you earned by working remotely in Minnesota is MN-source income, not MO-source income. Work income is "sourced" where the work is actually (physically) performed. MO taxes non-residents only on MO-source income. The employer's location does not determine sourcing.
This MO tax website explains the rules on whether or not you're required to file a MO tax return:
https://dor.mo.gov/taxation/individual/additional-resources/non-residents.html
Note that MO requires you to use the same filing status on your MO return (if you're required to file) that you used on your federal return.
ALL you & your husband's income is taxable by your home state of MN, regardless of where you earned it. It is almost always advantageous for married couples to file jointly.