Haw. Rev. Stat. § 235-93

(a) A husband and wife, having that status for purposes of the Internal Revenue Code and entitled to make a joint federal return for the taxable year, may make a single return jointly of taxes under this chapter for the taxable year. In that case the tax shall be computed on their aggregate income as provided in section 235-52, and the liability with respect to the tax shall be joint and several. For purposes of this chapter "aggregate income" means the income of both spouses without regard to source in the State.

(b) If an individual has filed a separate return for a taxable year for which a joint return could have been made by the taxpayer and the taxpayer's spouse, an election thereafter to make a joint return for the taxable year shall be made only upon compliance with rules of the department of taxation, which may limit the election and prescribe the terms and provisions applicable in such cases as nearly as may be in conformity with the Internal Revenue Code.

(c) The filing of a joint return after the individual has filed a separate return without full payment of the amount shown as tax on the joint return may be elected; provided all other requirements for the filing of a joint return under this section and the rules of the department are complied with. [L Sp 1957, c 1, pt of §2; am L Sp 1959 2d, c 1, §16; Supp, §121-27; HRS §235-93; am L 1974, c 9, §2; am L 1982, c 22, §1(4); am L 1997, c 297, §4]