How to count Thai tax surcharge under Revenue Code Section 27
Prepare the outstanding tax, user-confirmed month-or-part count and exclusions without mixing surcharge with penalties.
Keep surcharge separate from penalties
Section 27 covers surcharge when assessed tax is not paid or remitted on time. It is calculated from the tax due without including penalties. The tool therefore excludes penalties, criminal fines and other amounts.
Count each month or part from the actual period
The general Section 27 rate is 1.5% per month or part of a month, counted after the filing or remittance deadline through payment. Confirm the actual deadline and period count from the filing and Revenue Department channels; the tool does not infer dates.
The general result is capped
Section 27 caps the calculated surcharge at the amount of tax due or remitted. The calculator applies that cap to the entered outstanding tax.
Extensions and special provisions need separate review
Section 27 also states a reduced rate for an approved extension paid within the extended period. This version excludes that case, reductions, waivers and tax-specific provisions. Check the assessment, filing and current Revenue Department guidance.
Sources and scope
This guide explains how to prepare inputs within the tool's scope. It is not legal, tax, financial or academic advice.
Content and sources checked 21 September 2026