Effect Of Rate Changes During A Taxable Year

5.1. If the rate of personal income tax imposed by the West Virginia Personal Income Tax Act is changed to become effective after the thirty-first (31st) day of December of a calendar year, and if a taxpayer subject to the West Virginia Personal Income Tax Act has a taxable year which includes the effective date of the change (unless that date is the first day of the taxable year), then the following rules shall be observed in computing such taxpayer's rate of tax:

5.1.1. Tentative taxes shall be computed by applying the rate for the period before the effective date of the change, and the rate for the period on and after such date, to the taxable income for the entire taxable year; and

5.1.2. The tax for such taxable year shall be the sum of that proportion of each tentative tax which the number of months in each period bears to the number of months in the taxable year.

5.1.3. For puposes of this Section:

5.1.3.1. If the rate changes for taxable years beginning after or ending after a certain date, the following day shall be considered the effective date of the change; and

5.1.3.2. If a rate changes for taxable years beginning on or after a certain date, that date shall be considered the effective date of the change of rate.