Question 1

Certificate of tax residence (R.O.21 / R.O.22): You must prove Thai tax residence to a foreign tax authority

Accepted Answer

The Revenue Department. Variable, depending on how complete your filed returns are. Missing returns for the referenced year block issuance

Question 2

Claim relief under a double tax agreement: You earn income from a country with a treaty with Thailand

Accepted Answer

The Revenue Department and the counterpart tax authority. Variable, per the mechanism that country applies. Assuming a treaty exempts all tax — most allocate taxing rights or grant a credit

Question 3

Refund of over-withheld tax: Withholding exceeded the treaty rate

Accepted Answer

The tax authority of the withholding country. Highly variable — often several months. Missing the refund filing deadline forfeits the claim

Comparing cross-border tax routes

Certificate of tax residence (R.O.21 / R.O.22)

Claim relief under a double tax agreement

Refund of over-withheld tax

Let our advisers map the route

Route	When it applies	Certifying authority	Indicative timeline	Pitfalls / common rejections
Certificate of tax residence (R.O.21 / R.O.22)	You must prove Thai tax residence to a foreign tax authority	The Revenue Department	Variable, depending on how complete your filed returns are	Missing returns for the referenced year block issuance
Claim relief under a double tax agreement	You earn income from a country with a treaty with Thailand	The Revenue Department and the counterpart tax authority	Variable, per the mechanism that country applies	Assuming a treaty exempts all tax — most allocate taxing rights or grant a credit
Refund of over-withheld tax	Withholding exceeded the treaty rate	The tax authority of the withholding country	Highly variable — often several months	Missing the refund filing deadline forfeits the claim