The term "taxable year" with respect to any taxpayer means:

1. (1) The taxable year of such taxpayer required pursuant to the Internal Revenue Code; or
2. (2) Such other period as may be required by law; or
3. (3) The calendar year.

[63-3010, added 1959, ch. 299, sec. 10, p. 613; am. 1969, ch. 319, sec. 4, p. 982; am. 1997, ch. 57, sec. 1, p. 96.]