What are the tax implications and rates if I extend my DTV visa in Thailand?

First of all, taxation goes by calendar year. It's therefore not directly related to an extension of your DTV. If for instance you arrived in 2024, you're not immediately at 180 days in 2025 when your initial 180 days run out.

Second, Thailand's taxation is progressive, percentages varying from 0% to 35% in 5 percent point increments.

Then, whether or not you bring money in or leave it elsewhere will not matter in the future. It was one of the weirdest taxation features that has ever existed, and luckily it is gonna go. If you owe tax over income or components of you income in Thailand, by the applicable dual tax treaty, you owe regardless of where you keep the money.

And then lastly, already brought up by many others: how things play out in your situation is very hard to tell without more info, and requires professional expertise. It's for instance quite possible that you owe tax in Thailand by some DTA even if you do not stay 180 days in Thailand. Or the reverse: that you stay longer but that your income is not taxed in Thailand. The 180 days limit only has marginal relevance and is given way too much attention. The most important implication of the 180 days is that you must report your taxable income if you surpass it, which could also be 0 if your entire income is taxed elsewhere by the applicable DTA. Best to consult an expert.

Oh, and last last: taxation is not handled by immigrations but by the revenue department.

Here are the Thai income tax rates. If you stay 180 days you become a tax resident. Any money you bring into Thailand is assessable for potential tax. If your country has a Dual Taxation Agreement with Thailand, it may provide you with exemptions and allow you to off-set any income tax you paid in your own country. Look up the Thai Revenue Department for where you live and go see them for advice. You may be entitled to additional allowances in Thailand, which they would tell you about. They will not try to get money out of you that is not due. In fact I've now seen several reports where a rough assessment of income, like just a pension, led to a decision that they didn't need a TIN or submit a return.

@Nina ********

are you really really sure you will pay tax here? Why do you think like this? Seek professional advice

You seem very keen to pay tax. I'm assuming therefore that you're bringing in untaxed money?

Thai has progressive tax rates from 0-35%, the Revenue Department deals with taxation not the Immigration office.

No one here can answer your questions about taxes. You need to consult a tax expert to review your financial situation, how much money you remit to Thailand, as well as any relevant dual taxation treaties.

Extensions are done at your local immigration office. No one knows anything about DTV extensions as no one has gotten one yet.