The annualized income installment, in the case of any required installment, is the excess, if any, of:

(a) an amount equal to the applicable percentage of the tax for the taxable year computed by placing on an annualized basis the taxable income and minimum taxable income for months in the taxable year ending before the due date for the installment, over

(b) the aggregate amount of any prior required installments for the taxable year. The applicable percentage of tax, which will be computed without regard to any increase in the rates applicable to the taxable year unless such increase was enacted at least 30 days prior to the due date of the installment, will be as follows: The provisions of this subparagraph, with respect to determining an individual's annualized income installment for each installment period, can be illustrated as follows: Step 1: Annualized the taxable income and minimum taxable income for the months in the taxable year ending before the due date of the installment period and compute the tax due on this amount. Step 2: Multiply the tax computed in Step 1 by: 22½ percent if the payment due date is April 15th; 45 percent if the payment due date is June 15th; 67½ percent if the payment due date is September 15th; or 90 percent if the payment due date is January 15th of the following taxable year. Step 3: Figure the total of the required installments or annualized income installments for the preceding payment periods and subtract this amount from the amount in Step 2. Step 4: The result of Step 3 is the annualized income installment for the applicable installment period. If the annualized income installment for the installment period is less than the required installment, the individual need only pay such annualized income installment.