(1) A taxpayer qualifies for the disability income exclusion if they:

(a) are under age 65;

(b) are retired on disability;

(c) were permanently and totally disabled when they retired; and

(d) have not, for this or a prior tax year, treated their disability income as a pension or annuity.

(2) The adjusted gross income used in the computation of the exclusion is the taxpayer's Montana adjusted gross income computed without this exclusion.

(3) If the qualified taxpayer is married and files separately, the Montana adjusted gross income of the taxpayer and their spouse must be combined to compute the exclusion.

(4) The taxpayer must on the department's request provide satisfactory proof of disability. Satisfactory proof includes a document issued by a governmental unit, such as the Social Security Administration, certifying the taxpayer's permanent and total disability. If such certification is not available, the department may require other forms of verification that establish the taxpayer's permanent and total disability.