Is a Thailand tax health check worth doing, and what does it find?

01Filed is not the same as checked

Plenty of Chinese-invested companies in Thailand have books that were kept and returns that were filed, but nobody has ever put the two side by side.

That is what a tax health check does. It does not redo the bookkeeping. It reconciles the general ledger and the sub-ledgers against the returns already filed — VAT (PP.30 and PP.36), withholding tax (PND.1, PND.3, PND.53 and PND.54) and corporate income tax (PND.50 and PND.51) — item by item. Wherever the two do not tie is where the risk is sitting.

02What the check actually covers

Five areas, in the order they usually produce findings.

• Consistency between books and returns. Output VAT in the general ledger against PP.30 month by month; payroll in the books against PND.1; each withholding amount against the closing payable in the ledger. Wherever these do not tie, there is usually something unreported, reported in the wrong period, or reported on the wrong form.
• Input tax and voucher compliance. Whether input tax invoices carry a complete company name, the 13-digit tax ID and the head office marking (สำนักงานใหญ่). A non-compliant invoice means the input tax cannot be claimed, so this is the one item to check before any refund claim.
• How cross-border payments were treated. Every payment out of Thailand raises two questions at once: was the reverse VAT that was due paid (PP.36, filed by the 7th of the following month), and was the withholding tax that was due deducted (PND.54). In practice the most common failure is doing one and not the other.
• Revenue recognition and related-party dealings. Whether construction and long-term contracts are recognised on the percentage-of-completion basis (Por.73/2541) rather than carrying progress billings in full as deferred income; whether related-party lending is at market rates; and whether the related-party disclosure form is filed with the annual return once annual revenue reaches 200 million baht.
• Whether the reliefs are actually landing. BOI exemption, additional deductions, loss carry-forward — whether they were genuinely applied at the income tax filing end. A health check looks for what was missed as well as what was wrong.

03When it pays to do it

The first window is before the year-end close. Corporate income tax on PND.50 has to be filed within 150 days of the year end, alongside the statutory audit, so the large exposures — revenue recognition, cross-border withholding — have to be dealt with before the return goes in. Adjusting after that point costs you twice over.

The second is before a VAT refund claim. A refund application will almost certainly bring a Revenue Department review with it, so check input invoice compliance and the output reconciliation yourself before the claim is filed. See how much VAT you can get back and how long it takes.

The third is before a query or a signal that the Revenue Department wants to talk. If there are amended (ADD) filings in the record, or the filed figures do not agree with what your customers and suppliers reported, self-check first.

One practical detail that gets overlooked: Thai tax returns all use the Buddhist era. Subtract 543 to get the Gregorian year — 2569 is 2026. Do the conversion before deciding whether a return is late; a fair number of companies come unstuck on this exact step. See which returns fall due on which dates.

04Correcting it yourself, or waiting to be assessed

The cost of putting things right is a clear structure. Unpaid tax carries a surcharge of 1.5% per month (Revenue Code section 27), and an underreported withholding return carries a fine in the order of 1,000 to 2,000 baht per return. The longer it sits, the more the surcharge accumulates; and once a Revenue Department audit makes the finding, the penalty discretion is noticeably heavier than for a voluntary correction. The exact scale follows the official rules in force.

New discretion published in July 2026. The Revenue Department issued ท.ป.369/2569 and ท.ป.370/2569, updating the discretion applied to penalty reduction and giving clearer room for leniency to taxpayers who disclose voluntarily and cooperate in putting things right. For a company carrying historical exposure, this is a favourable moment to clear it. The extent of any reduction follows the official announcements.

05The checklist is generic; your exposure is not

The checklist is the same for everyone. The exposure is not — it lives in your own contracts, your own ledgers and your own approvals. Take one payment abroad: whether a treaty residence certificate exists, and how the income is classified, can lead to completely different conclusions on the same transaction. See what you have to withhold on payments to overseas service providers.

Whether a particular item should be corrected, how, and which return to correct first has to be settled by our advisers after going through your actual books and vouchers item by item.