Previously, Sections 57 Ter and 57 Quinque of the Revenue Code stipulated that if your marriage existed throughout the tax year, you and your spouse must file a joint tax return with the option that a wife may select to file her employment income (Section 40(1) income) separately.

However, on 4 July 2012, the Constitutional Court ruled that Sections 57 Ter and 57 Quinque of the Revenue Code are in breach of a constitution. Consequently, those two sections are no longer applicable. Hence, the government passed an Emergency Act that enacted Section 57 Sex of the Revenue Code in order to modify rules for married couples as follows:
 

Assessable Income

Income chargeable to the PIT is called "assessable income". The term covers income both in cash and in kind. Therefore, any benefits provided by an employer or other persons, such as a rent-free house or the amount of tax paid by the employer on behalf of the employee, is also treated as assessable income of the employee for the purpose of PIT. Assessable income is divided into 8 categories as follows :

1. You and your spouse can file a tax return jointly as before. However, while doing so, either spouse may also select to file his or her employment income (Section 40 (1) income) separately by filing another ภ.ง.ด.91 form, or
2. You and your spouse can file separate tax returns for all types of income received, and pay personal income tax separately. In case where certain income cannot be clearly identified as yours or your spouse’s, the following rules shall apply:
   1. For Sections 40(2) – 40(7) income, you and your spouse must divide the income received equally.
   2. For Section 40(8) income, as a general rule you and your spouse must divide the income received equally. Nevertheless, you and your spouse may agree upon the portion of income earned and pay income tax on that amount accordingly.

Deductible Expenses

The deductible expenses are split among the spouses in the same proportion as the joint income proportion

Allowances

Some allowances are calculated differently from tax year 2011. Main changes are as follows:

• Child allowance: Each spouse is entitled to 15,000 Baht (17,000 Baht if the child is studying at the qualified level)
• Home Loan Interest Deduction: Each spouse is entitled up to 100,000 Baht of interest deduction. However, if they enter into a loan agreement jointly, each of them is entitled to 50,000 Baht of interest deduction.

Filling Options

Pursuant to Section 57 Sex of the Revenue Code, a married couple may now have 5 options in submitting their tax returns:

1. Each spouse files his/her tax return separately;
2. The couple files their return jointly, combining the wife’s income with the husband’s income (and submit a return under the husband’s name);
3. The couple files their return jointly, combining the husband’s income with the wife’s income (and submit a return under the wife’s name);
4. The couple files their return jointly, but the husband files his Section 40(1) income separately;
5. The couple files their return jointly, but the wife files her Section 40(1) income separately.