Looking at this Gov link http://www.rd.go.th/publish/6045.0.html

Down the page a bit is "

Allowances (Exemptions) allowed for the calculation of PIT"

Are the amounts ,

a/ To come off the Gross annual income at the end of the year to calculate the new taxable income?

b/ The actual amount to reduce the amount of tax payable after the calculation?

eg:

Spouse allowance 30,000 baht Child allowance (child under 25 years of age and studying at educational institution, or a minor, or an adjusted incompetent or quasi-incompetent person) 15,000 baht each
(limited to three children) Education (additional allowance for child studying in educational institution in Thailand) 2,000 baht each child Parents allowance 30,000 baht for each of taxpayer’s and spouse’s parents if such parent is above 60 years old and earns less than 30,000 baht

I also tried to understand this but as you can see it is not very clear at all, also I read about a 20% fixed rate new corporate tax law that is to stay permanently so I would also be interested in some answers in plain English.

TAXABLE INCOME = Assessable Income - deductions - allowances

I don't fully understand the two options you are suggesting, but I think it is a).

Basically, you take your income, then subtract all the deductions, and all the allowances. This is then your taxable income, for which you apply the progressive tax rates in Section 3.1.

Question:

Are the amounts ,

a/ To come off the Gross annual income at the end of the year to calculate the new taxable income?

b/ The actual amount to reduce the amount of tax payable after the calculation?

Answer:

a/ Yes.

b/ No.

The amounts listed (if applicable) are deducted from your gross taxable income.

Calculate your income. Now deduct your allowances and deductions. Now calculate the tax payable on this amount.