Thailand Income Tax. Thailand’s personal income tax (PIT) regime is a residence-based system with several features that routinely surprise long-stayers, remote workers and people with cross-border assets: (1) a strict 180-day residency test; (2) a recent reinterpretation of taxation on foreign-sourced income brought into Thailand; and (3) a mix of withholding-tax options and targeted exemptions (notably for exchange-traded share gains). Below I map the rules that matter in practice, show how the remittance rule operates, and give concrete steps to be audit-ready.
Who is taxable (residency, source rules)
An individual is a Thai tax resident if they are present in Thailand for 180 days or more in a calendar (tax) year. Residents are taxed on (a) Thai-source income and (b) certain foreign-source income when it is brought into Thailand, subject to the detailed remittance rules below. Non-residents pay tax only on Thai-source income.
The statutory categories of assessable income follow the Revenue Code’s Section 40 (employment, professional fees, dividends, interest, rentals, gains, etc.). Classification matters because it determines withholding, allowable deductions, and whether certain final-tax options apply.
The remittance rule (DI Por.161 / DI Por.162) — what changed and the grandfathering
In late-2023 the Revenue Department issued Departmental Instruction No. Por.161/2566, which interprets Section 41 to make foreign-sourced income taxable when it is remitted into Thailand (even if earned earlier). This was a sharp departure from the long-standing practice that taxed foreign income only if remitted in the same year it was earned. Shortly after, DI Por.162/2566 clarified grandfathering: foreign income earned before 1 January 2024 is generally not caught by Por.161 when brought into Thailand from 2024 onwards — but income arising on or after 1 January 2024 is taxable when remitted. Because the rule turns on when the income arose and when it was remitted, documentary proof of the income’s origination date is decisive.
Practical consequence: remitting old savings built up before 2024 typically does not create a Thai PIT liability, but remittances of income/gains earned in 2024+ will. Keep dated bank statements, contracts and dividend advices to show when income arose.
Rates, bands and the basic computation
Thailand applies progressive PIT bands up to 35% for high earners (the standard bracket schedule in force covers 0% up to THB 150,000 and progressive steps up to 35% above the top band). Standard personal allowances, spouse/child allowances, social security deductions and prescribed expense rules apply when computing taxable income. Use annual tax bands and the official revenue forms (PND 90/91) to compute net taxable income.
Withholding taxes, elections and common traps
Thailand uses withholding (WHT) extensively:
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Dividends from Thai companies are subject to a 10% WHT; residents may elect to treat that WHT as final (exclude the dividend from the PIT return) or include the dividend and claim credit for the WHT.
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Interest and many passive payments have flat WHT options (commonly 15% on interest if it is treated as final, though technical exceptions apply).
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Payroll WHT is progressive and withheld monthly by employers.
Withholding choices matter: electing final WHT can simplify filing, but may be disadvantageous if your marginal rate is lower than the flat WHT rate or if you need the WHT as a credit against higher Thai tax on other income.
Capital gains — the key practical exemption
A very important practical relief: capital gains on shares sold on the Stock Exchange of Thailand (SET) and many exchange-traded fund units are exempt from PIT for individuals (sales off-exchange or gains on non-listed securities are treated as ordinary income unless a specific exemption/withholding election applies). This exemption often makes listed investing tax-efficient for resident individuals.
Foreign tax credit, DTAs and documentation
Thailand offers foreign tax relief under its double tax agreements (DTAs) or via domestic credit rules—but the availability and scope depend on the treaty wording and documentation. To claim credit, you typically need an official Tax Payment Certificate or equivalent from the source jurisdiction; the credit is limited to the Thai tax payable on that same income. Given the remittance rule, make sure any foreign tax payment is evidenced and contemporaneous with the income it purportedly taxes. The Revenue Department publishes guidance on acceptable documents and procedures.
Deadlines, forms and penalties
Annual PIT returns (PND 90/91) follow the calendar year. Paper returns are usually due 31 March; electronic filing windows are extended slightly into April (e-filing dates vary year to year — e.g., early April filings have been permitted in recent years). Withholding returns and half-year instalments follow separate schedules. Late filing or late payment attracts surcharges and interest; deliberate non-reporting can trigger audits and criminal exposure. Confirm the Revenue Department’s calendar each year.
Tactical examples
Example A — Remote worker / resident in 2025
You worked abroad in 2025, earned USD salary and kept it offshore; you remit part of it to Thailand in 2025. Because the income arose in 2025 (post-2024) and you are a Thai resident, the remitted portion is taxable in Thailand in 2025. Claim foreign tax credit where treaty or local rules allow.
Example B — Pre-2024 investment proceeds
You accumulated dividends in 2022 and bring the cash home in 2025. Under DI Por.162 the 2022-arising income should not be taxed on remittance in 2025 — retain dated brokers’ statements proving the 2022 origin.
Audit-ready checklist (what to keep)
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Residence evidence: passport stamps, flight records, tenancy or utility bills showing presence.
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Source-date proof for foreign income: contracts, pay advices, dividend statements with issue dates, bank credit advices showing the date income was generated.
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Foreign tax certificates: official receipts from foreign tax authorities; authenticated translations if needed.
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Withholding certificates: Thai and foreign WHT slips (to claim credits).
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Share transaction records: broker confirmations showing on-exchange trade dates (for SET exemption).
The remittance rule makes the timing documents the single most important evidentiary set in cross-border cases.
Final practical tips
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Treat the remittance rule as real: plan the timing of transfers and keep robust proofs of when income arose.
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If you have substantial foreign income earned in 2024+, get professional tax advice before remitting it.
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Use SET trading for retail equity exposure where appropriate; the on-exchange exemption can materially change after-tax returns.
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Keep copies of all tax payment certificates — they are the passport to foreign tax credit.