You stated: "We plan to change our domicile and make Utah our new domicile," which implies that you are still domiciled in California. Here are California's rules regarding change of domicile:
A change of domicile requires all of the following:
• Abandonment of your prior domicile.
• Physically moving to and residing in the new locality.
• Intent to remain in the new locality permanently or indefinitely as demonstrated by your actions.
https://www.ftb.ca.gov/forms/2020/2020-1031-publication.pdf
Here are the general principles:
Your state of domicile can tax ALL your income, regardless of its source. Other states can tax you only on income sourced within that state.
If your domicile changes during the tax year, you are a part-year resident of each of the two states for tax purposes. In this case you would allocate your retirement income between the two states according to when you received it. Retirement income is taxable by your state of domicile at the time you receive it.
If your domicile does not change during the tax year, for tax purposes you are a resident of your domiciliary state, and a non-resident of any other state in which you have a filing requirement. In that case your entire retirement income would be taxable by the domiciliary state.
Deferred work income is normally taxable by the state in which it was earned, as well as by the state of domicile when received (if different). If the income is taxable by two states, the domiciliary state will normally grant a credit for the taxes paid to the other state, so as to avoid double taxation.
You can only have one domicile at a time.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
