Before you start

A day count for the calendar year, kept as you go
Records of when foreign income was earned as well as when it was remitted
A Thai Tax Identification Number from the Revenue Department

Step-by-step

1
Count your days — the line is 180, not 183
180 or more days in Thailand within a single calendar year, consecutive or not, makes you a Thai tax resident for that year. Many people carry a 183-day rule of thumb from elsewhere and miscount by exactly three days. The count resets every 1 January. Because residency is what pulls remitted foreign income into scope, this number matters far beyond any Thai salary.
OnlineWho: YouTrack through the yearFree
2
Get a Tax Identification Number
Register with the Revenue Department for a TIN. Employees usually have HR arrange it; otherwise apply at a local Revenue Department area office. You need it to file and to use the online e-filing system. Having one also makes claiming treaty relief and evidencing your position substantially easier.
In personWho: You (employer's HR often assists)Same day to a few daysFree
3
Account for foreign income you remit into Thailand
Since 1 January 2024, foreign-sourced income earned while you are a Thai tax resident is assessable here when you remit it, whether that is the same year or ten years later. The pre-2024 practice of parking income offshore for a year and bringing it in tax-free is gone. Income earned before 1 January 2024 is outside the rule regardless of when you transfer it, which makes dated records of when funds were earned genuinely valuable. Thailand's treaty network may allow credit for foreign tax paid, but you generally have to claim and evidence it.
OnlineWho: You, ideally with a Thai adviserTrack continuouslyDepends on amounts and treaty relief
4
File the annual return
Thai personal income tax runs on the calendar year. File PND.91 if your only income is Thai employment, PND.90 if you have other or foreign income. Paper returns are due at the end of March, with a short extension for online filing through the Revenue Department portal. Employees have tax withheld monthly by their employer and still file to reconcile.
OnlineWho: YouFiled January to March following the tax yearFree to file; pay any balance due
5
Understand the property tax side before you buy
Buying or leasing here carries its own charges at the Land Department — transfer fees, lease registration fees, and, on a sale, taxes on the disposal. There is also an annual land and building tax at rates that differ for residential and commercial use. None of this is Phuket-specific in law, but Phuket is where foreigners most often encounter it, and the numbers are material on a villa or condominium. Budget for them separately from the purchase price.
In personWho: You, with your own lawyerAt transfer and annually thereafterLand Department transfer and registration fees plus annual land and building tax

Documents you’ll need

Thai Tax Identification Number
Employer withholding certificate, if employed in Thailand
Dated records of when foreign income was earned and when it was remitted
Evidence of foreign tax paid, for any treaty credit claim
Land Department documents and tax receipts, if you own property

Things most newcomers don’t know

The line is 180 days, and people who carry a 183-day habit from elsewhere miscount it every year.

Most countries use 183 days as the residency threshold. Thailand uses 180. Three days sounds trivial until you realise that crossing the line is what makes your remitted foreign income assessable here — so someone carefully managing their stay to just under what they believe the threshold is can land inside it without noticing. Count deliberately, keep the record, and be aware that days need not be consecutive and the count resets on 1 January.

Source: Thai Revenue Code residency test

Pre-2024 foreign income is grandfathered, and your records are the only thing that proves it.

Foreign income earned before 1 January 2024 is not assessable when remitted, regardless of when you bring it in. That makes dated evidence of when funds were earned — as distinct from when they were transferred — genuinely valuable, because it can keep older savings permanently outside the Thai tax net. Anyone who moved to Phuket with accumulated savings should document the position now, while the records are easy to obtain, rather than during an enquiry.

Source: Revenue Department orders Por. 161/2566 and Por. 162/2566

A promise to renew a 30-year lease beyond the statutory maximum is not enforceable against a new owner — and the leading case was a Phuket dispute.

Section 540 of the Civil and Commercial Code caps a lease of immovable property at thirty years. The widely-marketed '30+30+30' structure, in which a lessee pays up front for two further renewal terms, was tested in Supreme Court Decision 4655/2566 — arising from a Phuket land lease — which held that a pre-agreed renewal beyond thirty years cannot create a real property right. At best it binds the original landlord personally; a successor who buys the land is not obliged to honour it. If you are being sold a ninety-year leasehold villa, that is the risk you are actually taking.

Source: Civil and Commercial Code s.540; Supreme Court Decision 4655/2566

Condominium foreign quota and land ownership are two different questions, and the nominee-company 'solution' is unlawful.

A foreigner may own a condominium unit provided the building's foreign-owned share stays within the statutory limit measured on aggregate unit floor area — so a building can simply be full, and no amount of money changes that. Land is different: foreigners cannot own it. The structure widely marketed in Phuket, a Thai company with nominee shareholders existing only to hold land for a foreigner, is unlawful, and the exposure is loss of the asset rather than a fine. Take advice from a Thai lawyer you found independently, not one introduced by the seller.

Source: Condominium Act B.E. 2522; Thai land ownership restrictions on nominee shareholding

Common mistakes to avoid

Using a 183-day rule of thumb when Thailand's residency threshold is 180 days
Assuming foreign income is untaxed here because it was earned abroad — since 2024, remitting it as a resident can make it assessable
Failing to keep dated records showing which savings were earned before 2024 and are therefore outside the rule
Buying a leasehold villa sold as 30+30+30 without understanding that renewals beyond thirty years do not bind a successor owner
Accepting a nominee-shareholder company structure to hold land, which is unlawful and puts the asset at risk
Budgeting a property purchase without the Land Department transfer and registration fees, or the annual land and building tax

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.