(1) a parent and substantially controlled subsidiary or subsidiaries;

(2) two or more corporations under substantially the entire control of the same interest.

However, a corporation that has elected to be taxed under Subchapter S of the Internal Revenue Code may not join in the filing of a consolidated income tax return under this section.

The terms "substantially controlled" and "substantially the entire control" mean the ownership of at least eighty percent of the total combined voting power of all classes of stock of all corporations that are a party to a consolidated return.

(B) All corporations included in a consolidated return must be subject to tax under § 12-6-530.

(C) A corporation doing business entirely within this State may consolidate with a corporation doing a multistate business. Two or more corporations doing a multistate business may file a consolidated return.

(D) A consolidated return means a single return for two or more corporations in which income or loss is separately determined as follows:

(1) South Carolina taxable income or loss is computed separately for each corporation;

(2) allocable income is allocated separately for each corporation;

(3) apportionable income or loss is computed utilizing separate apportionment factors for each corporation;

(4) income or loss computed in accordance with items (1) through (3) of this subsection is combined and reported on a single return for the controlled group.

(E) All corporations included in a consolidated return or a combined return must use the same accounting year.

(F) If a corporation which files or is required to file a consolidated return is entitled to one or more income tax credits, including the carryover of unused credits from prior years, the income tax credits must be determined on a consolidated basis. Limitations on credits which refer to the income or the income tax liability of a corporation are deemed to refer to the income or income tax liability of the consolidated group, and credits shall reduce the consolidated group’s tax liability regardless of whether or not the corporation entitled to the credit contributed to the tax liability or of the consolidated group.

(G) The election to file a consolidated return or separate returns must be made on an original and timely return and may not be changed after the return is filed.

(H) Once an election is made to file a consolidated return, this election must be adhered to until permission is granted by the department to file separate returns.