By Kan Amornratwitaya, Associate Director – Tax & Accounting, Kreston Thailand
Every year, around this time, I get the same calls. A foreign executive realises the 31 March filing deadline is two weeks away. An HR manager discovers that three expat employees have never filed at all. A business owner asks me whether income earned overseas needs to be declared in Thailand. The answer to that last one is often yes and that surprises people more than it should.
If you are in Thailand and earning income, the deadline matters to you. Paper filing closes 31 March 2026. Online submission through the Revenue Department‘s e-filing system closes 8 April 2026. These are not soft deadlines. Missing them carries surcharges and penalties that are entirely avoidable.
The Mistake I See Most Often
The most common problem I encounter when reviewing a new client’s personal income tax position in Thailand is not fraud or deliberate evasion. It is simply not knowing what you are entitled to claim or claiming it incorrectly.
Taxpayers in Thailand regularly miss deductions they are fully entitled to use. LTF and RMF fund contributions are deductible up to specific limits and are one of the most effective tools available for reducing your taxable income yet many foreign residents either do not invest in them or do not realise they qualify to claim them. Spouse allowances and child allowances are routinely missed or miscalculated. Government-introduced special deductions the kind the Revenue Department announces periodically to stimulate spending in specific categories are almost never claimed by foreign clients because they simply did not know they existed.
The result is that people overpay. Not because the system is unfair, but because they filed without understanding what the system allows.
What I Have Seen
This applies to all taxpayers not just employees or business owners. I have reviewed returns from foreign nationals in Thailand who filed on time and believed everything was in order. When we went through the detail, they had claimed only the basic personal allowance and nothing else. No spouse allowance. No child allowances. No health insurance deductions. No LTF or RMF contributions despite holding qualifying funds.
The common thread is not carelessness. It is simply not knowing these deductions exist. They found a basic guide, followed the steps, and submitted. The guide told them how to file. It did not tell them what they were entitled to claim.
That gap between knowing how to file and knowing what to claim is where most foreign taxpayers in Thailand lose money.
Some People Do Not Know They Need to File at All
This one surprises people when I say it out loud, but it is more common than you would expect. Some foreign taxpayers in Thailand including people who have been here for several years simply do not know they are required to file a personal income tax return.
The assumption is usually that their employer handles everything through payroll withholding, so there is nothing left to do. Sometimes that is true. Often it is not. If you have income from more than one source, freelance or consulting income, rental income, or overseas income brought into Thailand, withholding tax alone does not close your filing obligation. You still need to file.
The Revenue Department does not always chase people immediately. But when they do, the penalties for late filing go back years. I have seen clients receive assessments covering multiple years at once. The tax itself is rarely the biggest shock it is the surcharges and penalties on top of it.
If you are unsure whether you are required to file, the answer is almost certainly yes. Check before the deadline, not after.
Keep Your Supporting Documents Ready
Claiming a deduction is one thing. Proving it is another. If the Revenue Department reviews your return, they will ask for documentation to support every item you have claimed. This is where many people find themselves in difficulty not because they claimed incorrectly, but because they cannot produce the evidence.
The documents you need to keep include health insurance premium receipts, fund house certificates confirming your LTF and RMF contributions, receipts for any government special deductions you have claimed, and any documentation supporting spouse or child allowances. Keep these for at least five years. Do not assume your employer, your bank, or your fund manager will have copies ready when you need them.
A Note for Foreign Nationals on Special Tax Privileges
Some foreign taxpayers in Thailand may be entitled to special tax privileges that significantly affect their personal income tax position. The Long-Term Resident visa, known as the LTR visa, comes with a flat personal income tax rate of 17 percent for qualifying holders working in Thailand. This is materially different from the standard progressive tax rates that go up to 35 percent.
If you hold or are considering an LTR visa, your tax position needs to be assessed separately. Do not assume the standard filing process applies to you in the same way. This topic deserves a full discussion on its own we will cover it in detail in a separate article.
Overseas Income: The Issue People Underestimate
Thailand’s personal income tax rules on overseas income changed significantly. If you are a Thai tax resident meaning you spend 180 days or more in Thailand in a calendar year income you bring into Thailand that was earned abroad may be assessable. This catches people off guard, particularly foreign business owners and executives who receive income from multiple countries.
I am not going to summarise the rules here in full because the details depend on your specific situation, your tax residency status, and applicable tax treaties. What I will say is this: if you have overseas income and you have not discussed it with a tax adviser, do not assume it does not need to be declared. That assumption is the one that creates problems later.
What to Do Before 8 April
If you have not yet filed, do not wait. The online deadline of 8 April gives you time, but not much. Use it.
Before you file, go through this list:
- Personal allowance (60,000 THB)
- Spouse allowance (60,000 THB if applicable)
- Child allowances (30,000 THB per child under qualifying conditions)
- Health insurance premiums for yourself and parents
- LTF and RMF fund contributions (if you hold qualifying funds)
- Any government special deductions announced for the 2025 tax year
- Overseas income brought into Thailand during 2025
If you are unsure about any item on that list, get advice before you file not after. Amending a return is possible but it takes time and creates questions you would rather not answer.
My Recommendation
Do not file your personal income tax return in Thailand based on a general guide. File it based on your actual situation. The allowances and deductions available under Thai tax law are specific, and the rules around overseas income have changed. A thirty-minute review with a tax adviser before you file will almost always save you more than it costs either in tax you should not have paid or in problems you should not have created.
One more thing for next year: submit your Lor Yor 01 form to your HR or payroll team at the start of the year. This form tells your employer which allowances and deductions you expect to claim, so they can calculate the correct monthly withholding tax. Do it properly and your withholding will match your actual tax position as closely as possible. No surprise bill at filing time. No waiting for a refund you should not have paid in the first place.
The deadline is 31 March for paper filing. 8 April for online submission. There is still time to get this right.
If you are unsure whether you have claimed everything you are entitled to, or if you have overseas income and are not certain how it should be treated, speak with our team before you file. Contact Kan at Kreston Thailand to review your personal income tax position before the deadline.