Lived in CA for the first 2 months of 2020 and in Michigan for 10 last months. Bonus for 2020 was paid in 2021. Employer treated the bonus as part CA income and part MI income, even though I lived in Michigan for ALL of 2021.
Your California bonus pay is taxable to both California (that's where you earned it) and to Michigan (that's where you received it).
California says "Sick leave, vacation pay, and bonuses earned by a nonresident for services performed in California are considered California source income. See the Appeal of Edwin O. and Wanda L. Stevens, 86-SBE-100, May 6, 1986."
See 3440 Sick Leave, Vacation Pay, Bonuses, and Severance Pay in California's Residency and Sourcing Technical Manual
Michigan residents are taxed on all income received while a MI resident.
did you work either remotely for the company from MI or from a MI location for the same company?
if not, it would seem the entire bonus was earned for the 2 months you worked in CA and should have been reported as such.
Isn't that double-taxation if I owe CA and MI for the same income? How can that be right?
Yes, worked for the same company for the whole year: 2 months in CA and 10 months in MI.
@salg8nor Yes it is double taxation which is why Michigan will give you a credit for tax paid to California on the Mi tax return.
In the Michigan section, you'll see the screen Take a look at Michigan credits and taxes.
In Other credits, select Other State Tax Credit. If you do your nonresident California return first, the numbers in this section will auto populate. If you started MI first, delete MI, complete CA, then add MI.