Who must file
For personal income tax, s.56 of the Revenue Code requires a return from anyone other than a minor or a person adjudged incompetent whose assessable income for the preceding tax year exceeded: THB 60,000 with no spouse; THB 120,000 with no spouse if the income was employment income under s.40(1) only; THB 120,000 with a spouse; or THB 220,000 with a spouse if the income was employment income only. That is a filing threshold, not a tax-free amount — it is far below the point at which tax is actually due. Use ภ.ง.ด.91 (PND.91) if all the income is employment income under s.40(1), and ภ.ง.ด.90 (PND.90) if any of it is not. A non-juristic ordinary partnership or body of persons files in its own name through its manager. Residents (more than 180 days in the calendar year) are taxed on Thai income and on foreign income brought into Thailand; non-residents on Thai-source income only. Companies and juristic partnerships file corporate income tax on ภ.ง.ด.50 (PND.50), with a half-year estimate on ภ.ง.ด.51 (PND.51).
Tax year and deadline
The personal tax year is the calendar year and the return is due on or before the last day of March in the following year (s.56). File it electronically at efiling.rd.go.th and the deadline moves to 8 April, under the Ministry of Finance internet-filing announcement, which currently covers returns due up to 31 January 2027. A half-year return, ภ.ง.ด.94 (PND.94), is due within September of the tax year itself from anyone with income under s.40(5) to (8) — rent, professional fees, contract work, business income — earned January to June; e-filing moves it to 8 October. Tax of THB 3,000 or more may be paid in three monthly instalments under s.64(1). For companies: PND.50 and the audited accounts are due within 150 days of the end of the accounting period, 158 days if e-filed, and the half-year PND.51 within 2 months of the end of the first six months, 2 months and 8 days if e-filed.
Filing step by step
- Register once for e-Filing at efiling.rd.go.th; the Revenue Department issues the username and password used for every return type.
- Gather the withholding tax certificates (หนังสือรับรองการหักภาษี ณ ที่จ่าย) from every payer, plus receipts for the allowances you will claim — provident fund, insurance, mortgage interest, parental support, donations.
- Pick the form: PND.91 if all your income is salary under s.40(1), PND.90 if any of it is not. The portal pre-fills much of the income and withholding data the Revenue Department already holds.
- Submit by 31 March, or by 8 April if you file online — but file the original and any amended return the same way. Mixing a paper filing with an electronic one for the same return forfeits the 8-day extension and leaves you liable for penalty and surcharge from the original deadline.
- Pay any balance at submission, by card, bank transfer, QR or counter payment, or elect the three-instalment option if the tax is THB 3,000 or more; track a refund through the portal's refund-status service.
Penalties for filing or paying late
For income tax, a person assessed under the Revenue Code by an official pays a fine equal to the tax due (section 22), or double the tax where the assessment follows a summons or is made on the official's best judgement because the taxpayer did not comply (section 26). Tax paid after its deadline also carries a surcharge of 1.5% per month or part of a month on the unpaid tax, counted from the day after the filing deadline until payment, and capped at the amount of tax owed (section 27); it is 0.75% a month if the Director-General approved an extension and payment is made within it. Giving false statements or evading tax is a criminal offence punishable by 3 months to 7 years in prison and a fine of THB 2,000 to 200,000 (section 37).