Depends on the "untaxed income". All income I earn in Australia is already subject to taxation, with the exception of pension which is exempt tax in Thailand. I have to declare any income earned in other countries on my Australian Tax return. However, if this is already taxed in another country, I am allowed credits against Australian Tax. I used to own an apartment in Germany on which I paid tax in Germany. I declared the income on my Australian Tax return, which made it "liable" to tax in Australia, but as I'd already paid in Germany, this offset anything I would have had to pay in Australia.
Doesn't quite work that way in all situations. Because of my situation, although I'm a dual tax resident, I am deemed to be tax resident solely of Australia. In this case Australia is my taxation authority, and Thailand is out of the loop, except as I say for money earned in Thailand
Anyone coming here for retirement purposes should get the 90-day non-O from their home country. I've no idea why people want to stuff around making the switch from a tourist visa or a visa exempt. I've never been able to figure that out
The minor changes to Thai taxation does not affect the DTA. Under the conditions of the Australian/Thailand DTA I am deemed an Australian Tax Resident, therefore only Australia can tax me on worldwide income. Thailand can only tax me on money which I earn inside Thailand, and as I'm retired that's a big fat zero. If I was earning money here, I would have to declare it on my Australian Tax return, although I would be able to apply tax credits, but that's irrelevant anyway