If a Thai has a Swiss brokerage account and is trading options on a US Exchange, where is tax paid? Does Thailand tax the gains? It is my understanding that when a foreigner is only "trading" in the US there is no US capital gains tax, but there could be and likely is tax in the home country. How does one go about finding a proper accountant or tax advisor in Thailand? Sunbelt, do you do this type of work?

AFAIK the broker needs to report the activities to the US IRS, as well as to the Tax authorities in the country of citizenship.

If a Thai has a Swiss brokerage account and is trading options on a US Exchange, where is tax paid? Does Thailand tax the gains? It is my understanding that when a foreigner is only "trading" in the US there is no US capital gains tax, but there could be and likely is tax in the home country. How does one go about finding a proper accountant or tax advisor in Thailand? Sunbelt, do you do this type of work?

It doesn't matter if he is trading from Switzerland or Thailand. Assuming that his Switzerland brokerage account is registered to his Thai address - he will be subject to Withholding Taxes per the Double Tax Agreement (DTA) between Thailand and the USA.

Generally speaking, the prescribed rate of Withholding Taxes between Thailand and the USA are :

(read here for the relevant DTA USA and Thailand)

- Interest Income: 5%

- Dividend Income: 10%

- Capital Gains: 30%

That being said, if the Income or Capital Gain is remitted to Thailand in the same year they were earned or gained, Thailand will levy taxes on the portion that was remitted inside Thailand. Although, Thailand will give a Foreign Tax Credit on the portion of the tax Withheld by the US.