If you're married and filing your Montana return separately, you can only exempt up to $800 of interest that you reported on your state return.
According to Line 3 -- Partial Interest Exemption for Taxpayers 65 and Older in the Montana Individual Income Tax Return (Form 2) Instructions:
If you are married and filing your return separately and are age 65 or older at the end of 2022, you can exempt up to $800 of the interest income that you reported in your Montana Adjusted Gross Income. Note, however, that you are not allowed to exclude interest income earned by and reported by your spouse.
