Do I have to pay tax in Belgium for my property in Thailand?

Janin, from your response I assume that you live in Belgium. After all, you are talking about a second home. But even then, Belgium is not allowed to levy taxes on your second home in Thailand. Not the Belgian national legislation, but the Treaty concluded by Belgium with Thailand, as a rule of international law and therefore of a higher order than national legislation, is decisive. In doing so, this Convention is based on the situs principle, involving a source state tax. To that end, see Articles 6 and 13, which I have quoted, and Article 22(1) of the Convention, which read as follows:

“Article 22 Power

1. Capital represented by immovable property as defined in paragraph 6 of Article 2 shall be taxable in the Contracting State in which such property is situated.”

Koen, read what you write yourself under point 3. It shows that my conclusion regarding real estate is correct. In addition, with AJ2022, the Treaty concluded by Belgium with Thailand has not been amended, while a Treaty, as a regulation of international law, takes precedence over national law.

Is there therefore no obligation to declare a second home located in Thailand?
Yes, there is a declaration obligation, but not because Belgium is allowed to levy tax on this property, but as a result of the progression reservation included in the Treaty. This progression reservation goes considerably further than what is customary and also covers income that is exempt in Belgium, such as due to an immovable property located in (in this case) Thailand.

See on this point Article 23(1) of the Convention and read as follows:

“Article 23 Exemption and settlement methods

1. In Belgium, double taxation is avoided in the following way:
a) If a resident of Belgium receives income which is taxable in Thailand under the provisions of the Agreement and to which the provisions of subparagraphs b), c), and d) below do not apply, or owns assets which are taxable under the provisions of are taxable in Thailand under the Agreement, Belgium shall exempt such income or assets from taxation. However, in calculating the amount of tax on the remaining income or capital of that resident, Belgium may apply the tax rate that would have been applicable if such income or capital had not been exempt.”

Freddy, even then a possible (second) home is not taxed in Belgium. However, this is different with regard to a possible bank balance in Thailand. However, I don't expect the latter to be the case.

With regard to a duty to declare in Belgium, see what I wrote in response to some responses to the progression reservation included in the Treaty (Article 23 of the Treaty).

Christian, I couldn't do anything with your first question. What can I do with “if you had a small business HERE” and “have a large amount in THAT bank account”.
And what should I do with the remark: "you can't get into trouble at all by giving up your home ownership and bank account."

The latter made me suspect that you have not yet filed a declaration in Belgium regarding a (possible) house and (possible) bank account in Thailand, while you now live in Belgium again and have now come to the conclusion that you can do this without you can still declare excessive financial consequences (“problem-free”) in Belgium.
You confirm this suspicion with your second message. So far you are committing tax fraud.

Subsequently, you cannot expect a self-respecting tax specialist to advise you on this. At most I can say: don't do that and stop doing it (regardless of the consequences)!

For clarity:
• If you live in Belgium, you must also indicate your foreign bank account.
• This also applies to a second home in Thailand and not to pay tax on it in Belgium, but to include it in the calculation of the tax due in Belgium on your other income (the progression reservation, which I wrote about earlier).

I assume that with a verifiable administration and with tax returns in Thailand due to your business activities there you can demonstrate the origin of your assets.
If not, you can certainly get into trouble, in the context of combating money laundering practices.

Incidentally, I note that such a matter does not really lend itself to being dealt with in a public forum!