Personal Income Tax (PIT) is a direct tax levied on the income of a person.  A person means an individual, an ordinary partnership, a non-juristic body of persons and an undivided estate.  In general, a person liable to PIT has to compute his tax liability, file tax return and pay tax, if any, accordingly on a calendar year basis.
Deductible expenses for the following income would increase from 40% of income (capped at 60,000 Baht) to 50% of income (capped at 100,000 Baht):
The scope of deductible expenses for income derived from under the section 40 (3) of the Revenue Code [Fee of goodwill, copyright or any other rights, annuity or annual payment of income derived from a will, any other juristic act, or court decision] – that was previously restricted only to copyrights, would expand to include goodwill, copyrights and other rights and will increase from 40% of income (capped at 60,000 Baht) to 50% of income (capped at 100,000 Baht).
I. For a taxpayer who has only employment income:
II. For a taxpayer who has employment income and other income, or who has only other income that is not employment income:
III. An undistributed estate must file a Tax Return if its income exceeds 60,000 Baht  (previously 30,000 Baht)
IV. A non-juristic partnership or a non-juristic body of persons must file a tax return if its income exceeds 60,000 Baht (previously 30,000 Baht).
Thus, based on the proposal above, if you are an employee and your monthly salary is 25,833 Baht or less, assuming that you do not receive other taxable income during the year (such as bonus or other fringe benefit), you will not have to pay Personal Income Tax.
