Legal service for foreign clients
Revenue Audit Defense & Assessment Appeals in Thailand
Answer summons, assemble evidence, and appeal inside the 30-day window.
Quick answer
When a summons arrives from the Revenue Department, the worst responses are silence and handing over unreviewed documents. Assessment officers may look back five years, and once a formal assessment notice is issued the taxpayer has just 30 days to appeal to the Board of Appeals. Miss it and the right lapses, leaving only limited recourse to the Central Tax Court.
From THB 25,000 — From THB 25,000 per issue; tax-court cases priced by amount in dispute · Officer stage 1–3 months; appeal stage 6–18 months
Who this is for
- Businesses summoned by an assessment officer
- Taxpayers assessed extra VAT or income tax
- Companies under deep review after a refund claim
- Firms with heavy related-party activity
What you receive
- Assessment of the officer's focus points and quantified exposure
- An explanation pack organized issue by issue
- Attendance at meetings for or alongside management
- PorSor6 appeal with full supporting evidence
Documents to prepare
- The summons or assessment notice
- Returns and statements for the years under review
- Related tax invoices and payment evidence
- Contracts proving the transactions were genuine
How it works
5-step process
- 1
Read the notice and diarize deadlines
Notice type, tax years, and reply dates are fixed at once.
- 2
Run an internal review first
Weak points are found before the officer sees them.
- 3
Explain and negotiate
Evidence is presented issue by issue to shrink the disputed amount.
- 4
Appeal when required
File PorSor6 within 30 days and consider a payment stay.
- 5
Litigate at the Central Tax Court
If the ruling is unfair, file within 30 days of receipt.
In depth
Revenue Audit Defense & Assessment Appeals: what foreign clients need to know
A summons from an assessment officer is not a verdict; it is the start of a process whose outcome turns mostly on documents and the order in which explanations are given. Businesses with customer disputes or court-ordered damages payments always face the follow-on question of whether that outlay is deductible. We work both sides at once: defending the tax base and recording it in a way that stands up.
Damages from disputes and consumer claims as a tax deduction
Compensation paid to a customer under a settlement or judgment is generally deductible if it relates to ordinary business activity and the file is complete: the settlement agreement, the judgment, proof of payment, and evidence tying the loss to the company's goods or services. The frequent failure is paying cash with no receipt stating the reason, which loses the deduction.
Statutory fines and penalties are non-deductible, unlike civil damages paid to a counterparty. Splitting the two at the point of entry matters, because when they sit in one account a reviewer tends to disallow the whole balance and leave the company to prove otherwise.
The stages of a tax review and what to do at each
It typically begins with a request for documents or an invitation to explain, moves to a notice of assessment if differences remain, then to an appeal before the appeal commission within the statutory window, and finally to the Tax Court if the appeal fails. Every stage has a hard deadline, and missing one forfeits the right without the merits ever being heard.
The explanation stage is the cheapest and the most likely to end the matter. Send only what was requested, with an explanation that cites document numbers; do not dump unsorted files and do not volunteer statements beyond the question, because what is recorded here follows you to the appeal and the court.
Preventing a repeat assessment the following year
The recurring assessment issues are few: expenses without original supporting documents, input VAT claimed on defective invoices, revenue recognised in a different period from the return, and cash on hand inconsistent with recorded sales. Once a case closes we fix the system, not merely the year that was reviewed.
What actually works is unremarkable but consistent: reconcile output VAT to revenue monthly, vet input invoices before posting rather than at year-end, keep commercial evidence beside receipts for large expenses, and review related-party items once a year.
Cost structure: government fees vs professional fees
| Item | Official fee | Professional fee | Note |
|---|---|---|---|
| Risk assessment and assembling the response file | No fee at the explanation stage | THB 20,000–60,000 | Includes attending the first meeting with you |
| Appealing an assessment to the appeal commission | No filing fee, though the statutory surcharge continues to run | THB 60,000–180,000 | Driven by the number of issues and tax years assessed |
| Litigating in the Tax Court | Court fees are calculated on the amount in dispute | THB 120,000–450,000 | Weigh the disputed amount against litigation cost before filing |
A retailer whose customer-compensation costs were disallowed in full
Situation: Statutory fines had been booked in the same account as damages paid to customers
What we did: We separated the items invoice by invoice, cited the settlements and payment evidence, and argued only the genuinely business-related portion
Outcome: The assessment reduced to the fines alone, which the law does not allow as a deduction
A service provider recognising revenue in a different period from its returns
Situation: Project revenue was invoiced in a different month from the ledger entry
What we did: We produced a month-by-month reconciliation showing a timing difference rather than unreported revenue
Outcome: Closed at the explanation stage with a timing adjustment and no additional revenue assessed
When to act, and when waiting is fine
You have received a request for documents or an invitation to attend
Reply within the deadline with only what was requested, and do not attend without a prepared explanation
An assessment notice has arrived and you disagree
Diary the appeal deadline the day the notice is received; that period cannot be extended
You paid damages to a customer this year
Separate damages from fines in the ledger and keep the settlement with the payment evidence
The disputed amount is smaller than the cost of fighting
Consider closing at the explanation or appeal stage and spend the budget on fixing the documentation system
FAQ
Frequently asked questions
Must tax be paid before appealing?
In principle yes, or request a stay with security, otherwise enforcement may follow.
How far back can they audit?
Normally two years, extendable to five where returns are believed incorrect.
How are surcharge and penalty computed?
Surcharge is 1.5% monthly; penalties vary by offence and may be reduced on request.
Must the assessed tax be paid before appealing?
An appeal does not automatically suspend the debt, so discuss security or instalments alongside filing it.
How many years back can the Revenue Department review?
It depends on the tax type and the circumstances; suspected under-reporting reaches back further than an ordinary review.
What if documents have been lost?
Circumstantial evidence can be used — bank statements, purchase orders, counterparty confirmations — together with an explanation of how they were lost.
Can the bookkeeper attend on our behalf?
They can and should attend, but bring someone responsible for the tax-law position from the first meeting.
Related services
Administrative & Tax Court Litigation
When an official order or a tax assessment is wrong, the law still gives you a route.
Tax Health Check Before the Revenue Calls
Find and close exposures early — far cheaper than an assessment.
Corporate & Personal Tax Planning
Lower tax through statutory reliefs, never through evasion.
Written by: Thai Law & Accounting Services — attorneys and licensed accountants
Reviewed by: Reviewed by a Notarial Services Attorney registered with the Lawyers Council of Thailand.
Last updated: 2026-08
Information as of August 2026. Government fees and processing times change — verify with the relevant agency before acting, or let our team verify for you.