Calendar year
(4) Calendar year. Calendar year means a period of 12 consecutive months ending on December 31. A taxpayer who has not established a fiscal year must make its return on the basis of a calendar year. (5) Fiscal year(i) Definition. Fiscal year means (A) A period of 12 consecutive months ending on the last day of any month other than December; or (B) A 52-53-week taxable year, if such period has been elected by the taxpayer. See 1.441-2. (ii) Recognition. A fiscal year will be recognized only if the books of the taxpayer are kept in accordance with such fiscal year. (6) Grandfathered fiscal year. Grandfathered fiscal year means a fiscal year (other than a year that resulted in a three month or less deferral of income) that a partnership or an S corporation received permission to use on or after July 1, 1974, by a letter ruling (i.e., not by automatic approval). (7) Books. Books include the taxpayer's regular books of account and such other records and data as may be necessary to support the entries on the taxpayer's books and on the taxpayer's return, as for example, a reconciliation of any difference between such books and the taxpayer's return. Records that are sufficient to reflect income adequately and clearly on the basis of an annual accounting period will be regarded as the keeping of books. See section 6001 and the regulations thereunder for rules relating to the keeping of books and records. (8) Taxpayer. Taxpayer has the same meaning as the term person as defined in section 7701(a)(1) (e.g., an individual, trust, estate, partnership, association, or corporation) rather than the meaning of the term taxpayer as defined in section 7701(a)(14) (any person subject to tax).