11 C.F.R. § 9002.12

Expenditure report period means, with respect to any Presidential election, the period of time described in either paragraph (a) or (b) of this section, as appropriate.

(a) In the case of a major party, the expenditure report period begins on September 1 before the election or on the date on which the major party's presidential nominee is chosen, whichever is earlier; and the period ends 30 days after the Presidential election.

(b) In the case of a minor or new party, the period will be the same as that of the major party with the shortest expenditure report period for that Presidential election as determined under paragraph (a) of this section.