Is tax payable on the profit from selling a business or a property in Thailand?

yes

Of course.

'Yes' and 'Of course' doesn't tell me much. Does anybody know what are the specifics? Under what circumstances must one pay capital gains tax and how is it calculated?

there is not a specific tax for capital gains, in Thailand. However gains made from the sale of Thai assets are (usually)  taxable and would be part of your Thai INCOME tax liability. Depending on the circumstances and the nature of the asset, on which the gains have been made, and also the level of your other Thai income. 

There can be some complexity around the calculation of the tax liability. really best to get some specialist advice;

any better?

Edited January 31, 20197 yr by wordchild

certain assets are exempt eg SET traded Thai shares.

If they are traded "on-market" (ref the long running legal saga of Thaksin and his Shin Corp shares).

Edited January 31, 20197 yr by wordchild