The instructions for the OK non-resident return state:
The Oklahoma taxable income of a part-year individual or nonresident individual shall be calculated as if all income were earned in Oklahoma, using Form 511-NR. The Federal Adjusted Gross Income (AGI) will be adjusted using the Oklahoma adjustments, allowed in 68 Oklahoma Statutes (OS) Section 2358, to arrive at AGI from all sources. The AGI from all sources is used to determine the taxable income. After the taxable income is calculated, it is prorated using a percentage of the AGI from Oklahoma sources divided by the AGI from all sources. This prorated tax is the Oklahoma tax.
So, yes, it looks like your tax (line 15a form 511-NR) is derived from all your income (Line 14 form 511-NR); however, on line 18 (form 511-NR) a ratio is calculated (state income as a percentage of all income), and on line 19, your actual state tax is reduced by this percentage.
So when TurboTax asks you what income is from Oklahoma sources, be sure to answer this.
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