How do I know how much I owe in each state?
Residents pay tax on all of the income (from all sources) they received during the calendar year. Residents get a tax credit for taxes paid to any other states.
Example: A California resident receives $20,000 from a rental building in Arkansas. The resident reports only the $20,000 to Arkansas and pays $2,000 in tax to Arkansas. Since the person is a California resident, California also taxes the $20,000, but gives a $2,000 tax credit for the tax you paid to Arkansas.
Part-year residents follow each state's rules. Some states separate the income, and tax only their state's income. Or a state may calculate the tax on all income as if you were a resident, and then allocate the tax based on "in state sources/all sources."