The tax year is the calendar year.
All persons earning income are required to file a tax return no later than 31 March of the following year for hardcopy filing and 8 April for online filing, except for individuals whose income from employment is THB 120,000 or less (for single persons) or THB 220,000 or less (for married persons) and in the case of having income from other sources (with or without employment income) of THB 60,000 or less (for single persons) or THB 120,000 or less (for married persons).
Individuals engaged in most forms of business are also required to file a return of their income for the first six months of the year by 30 September and pay the tax due.
Each husband or wife earning income can choose to file their income tax return either separately or jointly with their spouse, whichever they prefer.
Payment of tax
Income tax is required to be withheld at source from payments of salaries, other employment benefits, and certain other categories of income. The balance of any tax due for a calendar year is payable at the time of filing the annual tax return.