(a) Prepaid dues income for which an election has been made under section 456 shall be included in gross income over the period of time during which the liability to render services or make available membership privileges exists. The liability to render the services or make available the membership privileges shall be deemed to exist ratably over the period of time such services are required to be rendered, or such membership privileges are required to be made available. Thus, the prepaid dues income shall be included in gross income ratably over the period of the membership contract. For example, Corporation X, a membership organization, which files its income tax returns on a calendar year basis, elects, for its taxable year beginning January 1, 1961, to report its prepaid dues income in accordance with the provisions of section 456. On March 31, 1961, it sells a 2-year membership for $48 payable in advance, the membership to extend from May 1, 1961, to April 30, 1963. X shall include in its gross income for the taxable year 1961 8/24 of the $48, or $16, and for the taxable year 1962 12/24 of the $48, or $24, and for the taxable year 1963 4/24 of the $48, or $8.

(b) For purposes of determining the period or periods over which the liability of the taxpayer exists, and for purposes of allocating prepaid dues income to such periods, the taxpayer may aggregate similar transactions during the taxable year in any reasonable manner, provided the method of aggregation and allocation is consistently followed.