For taxable years beginning in 1989 and thereafter.

(1) An amount equal to the itemized deduction otherwise allowable under section 615(a) of the Tax Law (see section 115.1 of this Part) multiplied by 25 percent, the product of which is multiplied by a fraction, the numerator of which is the lesser of $50,000; or

(i) for an unmarried individual, other than a head of household or a surviving spouse, or married individual filing a separate New York State personal income tax return, the excess of such individual's New York adjusted gross income over $100,000;

(ii) for a married individual filing a joint New York State personal income tax return or a surviving spouse, the excess of such individual's New York adjusted gross income over $200,000;

(iii) for an individual who is a head of household, the excess of such individual's New York adjusted gross income over $150,000; and the denominator of which is $50,000.