My part-time resident Montana State tax return is using my total federal taxable income, despite correctly entering Montana sourced income in a previous step.

[MaryK4]

Montana part-year returns calculate tax liability based on total federal income first, then apply a ratio to tax only the Montana-sourced portion.

Part-year residents are subject to Montana income tax only on income attributable to state sources.  See Montana Residency.

[will-myers08]

I see, after doing the math myself I see that the part year ratio and correct calculations are occurring in the background, thank you.