(a) The income limits for filing joint or separate returns by a married couple are set out in Section 18501 of the Revenue and Taxation Code. Procedures and rules for filing joint or separate returns by a married couple are set out in Section 18521 of the Revenue and Taxation Code. For filing a joint return after filing a separate return see Sections 18522 and 18526 of the Revenue and Taxation Code.

(b) A joint return of a husband and wife shall be signed by both spouses, except that one spouse may sign the return as the agent for the other, if the return is accompanied by a power of attorney authorizing such action. The spouse acting as agent shall, with the principal, assume the responsibility for making the return and incur liability for the penalties provided for erroneous, false or fraudulent returns. The spouse who prepares the joint return of husband and wife shall execute the declaration that the joint return is made under penalties of perjury. The spouse who fills in the return shall be considered to have prepared the return. If the return is prepared by both spouses, or by neither spouse, then both spouses shall execute said declaration. Exceptions to both spouses signing are applicable to both spouses executing said declaration.

(c) If a separate return is filed by a resident married couple, each must report income from his or her separate property. Each must also report one-half of any community income, e.g., wages, salaries, and other compensation for personal services performed by either or both spouses; one-half of the income from community property owned, etc. If the husband and wife are separated and choose to file separate returns, then the entire earnings of each spouse is reported separately.

(d) Whether the income of a married couple who are nonresidents of this state must be reported by the husband or wife if a separate return is filed depends upon the spouse's domicile and the character of the income. Whether, in what fashion and to what extent income belongs to an individual spouse depends upon the character of the income. The character of the income is determined by the law of the state of domicile of the spouse earning the income.