These treaties often exempt foreign-source income from tax or provide credit for taxes already paid to the source country. 

Thailand has 61 Dual Tax Agreements. 

If the source country for your income transferred into Thailand has a DTA, you should carefully examine the specific DTA articles to find if you are entitled to a:

•     Tax credit,
•     Tax exemption,
•     Reduced rate of tax, or
•     Other treaty benefit or safeguard.

NOTE: They ARE NOT all the same! For example, the USA DTA exempts pensions for government service and social security from being taxed in Thailand (Articles 20 & 21). Whereas, the UK DTA only provides for the exemption of pensions for government service (Article 19). It does not exempt the UK State Pension although it is similar to the USA social security payments.

Click here for the Thailand Revenue Department's (TRD's) webpage that lists these countries.

Thailand has DTAs with the following countries which make up many of the English speaking Expats living in Thailand: Australia (1989), Canada (1985), Great Britain & Northern Ireland  (1981), Ireland  (2015), New Zealand (1998), and United States of America (1997).   This TRD page has links to the respective Agreements.

Click here for the TRD's Introduction to DTA page. The following is an excerpt from that page:

In general the DTA does not stipulate any specific item of income and tax rate. It provides whether the source or resident country is entitled to tax certain income. If the source country has taxing rights, the income will be subject to tax according to the domestic laws of that country.

Elimination of double taxation

The focus of a DTA is the elimination of double taxation. Each DTA may prescribe different methods of elimination of double taxation of a person by the resident country:

(1)   Exemption method*

The country of residence does not tax the income which according to the DTA is taxed in the source country.

(2)   Credit method

The resident country retains the right to tax the income which was already taxed in the source country. It calculates its tax on the basis of the taxpayer's total income including income from the other country which according to the DTA is taxed in that other country. However, it allows a deduction from its own tax for the tax paid in the other country.