Is the 800k you bring in for your retirement visa taxed? The money originates from the UK and is pension income and savings. Does this mean the additional 680k THB on top of the 120 is taxable in Thailand?

It depends on the source of the money that you remit and whether they are classed as foreign sourced income. Thailand tax residents are liable for taxes on their foreign-sourced income remitted to Thailand. This means if you’re considered a tax resident in Thailand—defined as someone who spends 180 days or more in the country in a calendar year—you must include your income remitted from abroad in your annual tax return and pay Thai taxes on it. However, to avoid double taxation (paying taxes on the same income in both Thailand and the country where the income was earned), Thailand has double tax treaties with 61 countries that allow for tax credits or exemptions. It’s important to consult a tax professional to understand how these treaties may apply to your situation and to ensure compliance with Thai tax laws while maximising available benefits.