26 CFR § 1.6153-3 - Short taxable years.
In the case of a short taxable year of an individual for which a declaration is required to be filed the estimated tax shall be paid in equal installments, one at the time of filing the declaration, one on the 15th day of the 6th month of the taxable year and another on the 15th day of the 9th month of such year unless the short taxable year closed during or prior to such 6th or 9th month, and one on the 15th day of the 1st month of the succeeding taxable year. For example, if the short taxable year is the period of 10 months from January 1, 1955, to October 31, 1955, and the declaration is required to be filed on or before April 15, 1955, the estimated tax is payable in 4 equal installments, one on the date of filing the declaration, and one each on June 15, September 15, and November 15, 1955. If in such case the declaration is required to be filed after April 15 but on or before June 15, the tax will be payable in 3 equal installments, one on the date of filing the declaration, and one each on September 15, and November 15, 1955. The provisions of paragraph (a)(3) of § 1.6153-1, relating to payment of estimated tax in any case in which the declaration is filed after the time prescribed in section 6073 and §§ 1.6073-1 to 1.6073-4, inclusive, are equally applicable to the payment of the estimated tax for short taxable years.