Before you start

Count your days: 180+ days physically in Thailand during the calendar year (1 Jan-31 Dec) makes you a tax resident for that whole year — keep your own log, as immigration stamps are the proof.
A Thai Tax ID (TIN) — issued same-day at your local (amphoe) Revenue Office; bring passport, visa/entry stamp, and proof of Chiang Mai address (lease + TM30). Required before you can file or claim treaty relief.
Records of foreign-source remittances: dates and amounts of every transfer into Thailand, plus evidence of what each transfer represents (pre-2024 savings vs. post-2024 income), since the tax hinges on remittance, not earning.

Step-by-step

1
Confirm tax residency and get a Thai Tax ID (TIN)
Tally your days in Thailand for the calendar year; at 180+ you are a tax resident and should register for a TIN. Go to the Chiang Mai Area Revenue Office covering your registered address with passport, a copy of your visa/entry stamp, and proof of address (lease + TM30 receipt). The TIN is typically issued the same day, free. Employees on Thai payroll are auto-assigned a TIN within 60 days of first income; remote workers/nomads must request one proactively.
In personWho: You (or an accountant with power of attorney); Thai-employed staff via employerSame day at the office; bring originals + copiesFree; agent/accountant assistance ~1,000-3,000 THB if used
2
Determine what foreign income is taxable on remittance
Apply the current Por. 161/162 rule: foreign-source income (remote-work pay, freelance, dividends, rent, capital gains) earned on or after 1 Jan 2024 and remitted into Thailand while you are a tax resident is assessable in the year you bring it in — the timing of earning no longer exempts it. Money clearly earned/saved BEFORE 1 Jan 2024 and remitted now is generally not taxed (Por. 162 grandfathers pre-2024 funds). The 2025 'same-year/following-year' exemption proposal was NOT in force as of mid-2026, so don't rely on it for the 2025 tax year. Map each remittance to a category and check the relevant double-tax treaty for foreign tax credits.
OnlineWho: You, ideally with a Thai tax advisor for cross-border / treaty questionsOngoing through the year; reconcile before filing season (Jan-Mar)Self: free. Advisory review of remittances ~5,000-20,000 THB
3
File the annual return (PND 90 or PND 91)
File for the prior calendar year using PND 91 (employment income only) or PND 90 (other/mixed income, including foreign remittances, rental, dividends). Apply allowances/deductions: 60,000 THB personal allowance, spouse 60,000 THB, up to 30,000 THB per child (max 3), plus mortgage interest, insurance, and provident-fund deductions where eligible. The first 150,000 THB of net income is taxed at 0%. Paper filing closes 31 March; online e-filing via rd.go.th extends to ~8-9 April. Even with zero tax due, file if you had assessable income.
OnlineWho: You (e-file on rd.go.th) or your accountant31 March (paper) / ~8 Apr (online) for the prior year; refunds take weeks to a few monthsFiling free; accountant for a foreigner's return with foreign income ~3,000-15,000 THB
4
Handle home-country obligations and double-tax relief
Being Thai tax resident does not end home-country duties. US citizens must still file a US federal return on worldwide income regardless of residency, plus FBAR (FinCEN 114) if foreign accounts exceed US$10,000 aggregate, and FATCA Form 8938 if thresholds are met; the US-Thailand tax treaty and the foreign tax credit (Form 1116) prevent most double taxation. Residents of treaty countries can claim a credit in Thailand for foreign tax already paid (or vice versa) — keep proof of tax paid abroad. Coordinate the two systems before remitting large sums.
OnlineWho: You, plus a cross-border accountant (especially US persons)US: 15 April (auto-extension to 15 June for those abroad); Thailand: see step 3US expat return prep ~US$300-800+ depending on complexity

Documents you’ll need

Passport with current visa/entry stamp (and prior stamps to evidence days of presence)
Thai Tax ID (TIN) card or number
Proof of Chiang Mai address: lease agreement + TM30 receipt
Records of every remittance into Thailand (date, amount, source) with documentation showing pre-2024 vs. post-2024 origin
Foreign income statements / payslips / dividend & interest statements
Evidence of foreign tax paid (for treaty / foreign tax credit claims)
Deduction support: insurance premiums, provident fund, mortgage interest, child/spouse details

Things most newcomers don’t know

The famous 'park it offshore for a year, then bring it in tax-free' loophole is dead — and the 2025 fix that would have softened it was never enacted.

Under the pre-2024 regime, foreign income was taxed only if remitted in the same year earned, so deferring remittance to a later year made it tax-free. Order Por. 161/162 (effective 1 Jan 2024) makes any post-2024 foreign income taxable in the year it is remitted, whenever earned. The Revenue Department's 2025 proposal to exempt income remitted in the same or following year stalled amid Thailand's political upheaval and was not in force as of mid-2026 — so your 2025 return follows the stricter Por. 161/162 rule. Treat any 'it's exempt now' claim with caution and verify the current status.

Source: Thai Revenue Department Orders Por. 161/2566 & 162/2566; Forvis Mazars analysis 2025-2026

DTV and digital-nomad money is not automatically tax-free — if you live in Chiang Mai 180+ days and remit your remote-work pay, it can be assessable.

The DTV governs your right to stay, not your tax status; the two are independent. Cross the 180-day line and you are a Thai tax resident, and remote-work income you bring into Thailand from post-2024 earnings is assessable under Por. 161/162. Many nomads assume foreign income is invisible to Thailand and skip filing — but with TIN-linked banking and CRS data-sharing, that gap is closing. Treaty relief often reduces the bill, but only if you actually file and claim it.

Source: Thai Revenue Department PIT rules (rd.go.th); Por. 161/162

Bring in your pre-2024 savings first — they are generally tax-free, which can fund a resident year cleanly.

Por. 162 grandfathers income earned and held before 1 Jan 2024: remitting those savings now is generally not taxed. Sequencing matters — fund your Thai living costs from clearly-documented pre-2024 capital rather than fresh post-2024 income, and keep bank records that distinguish the two. Without documentation, the Revenue Department may treat a remittance as current-year assessable income.

Source: Thai Revenue Department Order Por. 162/2566; PwC / Sherrings analysis

Common mistakes to avoid

Assuming your visa decides your tax — it doesn't. Residency is purely the 180-day physical-presence count, so a tourist-stamp or DTV stay over 180 days still makes you a tax resident
Believing the 2025 'same-year/following-year' exemption is law — as of mid-2026 it was an unenacted proposal; relying on it for your 2025 filing risks underpayment and penalties
Not filing because 'no tax is due' — if you had assessable income you must still file PND 90/91 by the deadline even when allowances zero out the tax
Remitting fresh foreign income without documenting whether it is pre-2024 savings (generally untaxed) or post-2024 income (taxable) — poor records let the tax office treat it all as assessable
US citizens assuming Thai residency ends US obligations — US returns, FBAR, and FATCA still apply on worldwide income

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