26 CFR §1.6655-3

1. (a)In general. In the case of any required installment, the amount of the adjusted seasonal installment is the excess (if any) of—
   1. (1)100 percent of the amount determined under paragraph (c) of this section; over
   2. (2)The aggregate amount of all prior required installments for the taxable year.
2. (b)Limitation on application of section. This section applies only if the base period percentage (as defined in section 6655(e)(3)(D)(i) and paragraph (d)(1) of this section) for any six consecutive months of the taxable year equals or exceeds seventy percent.
3. (c)Determination of amount. The amount determined under this paragraph (c) for any installment will be determined in the following manner—
   1. (1)Take the taxable income for all months during the taxable year preceding the filing month;
   2. (2)Divide such amount by the base period percentage for all months during the taxable year preceding the filing month;
   3. (3)Determine the tax on the amount determined under paragraph (c)(2) of this section; and
   4. (4)Multiply the tax computed under paragraph (c)(3) of this section by the base period percentage for the filing month and all months during the taxable year preceding the filing month.
4. (d)Special rules
   1. (1)Base period percentage. The base period percentage for any period of months is the average percent that the taxable income for the corresponding months in each of the three preceding taxable years bears to the taxable income for the three preceding taxable years. If there is no taxable income for the corresponding months, taxable income for this purpose is zero.
   2. (2)Filing month. The term filing month means the month in which the installment is required to be paid.
   3. (3)Application of the rules related to the annualized income installment method to the adjusted seasonal installment method. The rules governing the computation of taxable income (and resulting tax) for purposes of determining any required installment payment of estimated tax under the annualized income installment method under § 1.6655-2 apply to the computation of taxable income (and resulting tax) for purposes of determining any required installment payment of estimated tax under the adjusted seasonal installment method.
   4. (4)Alternative minimum tax. The amount determined under paragraph (c) of this section must properly take into account the amount of any alternative minimum tax under section 55 that would apply for the period of the computation. The amount of any alternative minimum tax that would apply is determined by applying to alternative minimum taxable income, tentative minimum tax, and alternative minimum tax, the rules described in paragraph (c) of this section for taxable income and tax.
5. (e)Example. The provisions of this section may be illustrated by the following example:
6. (f)Effective/applicability date. This section applies to taxable years beginning after September 6, 2007.