What every invoice must show
- The words ใบกำกับภาษี ('Tax invoice') in a prominent place, and the whole invoice in Thai, in Thai baht, and in Thai or Arabic numerals — a foreign language or currency needs the Director-General's approval (s.86/4).
- The 13-digit taxpayer identification number of the seller, and also of the buyer where the buyer is VAT registered. The buyer's number has been compulsory on full-form tax invoices since 1 January 2015 (Director-General Announcement on VAT No. 199).
- Which establishment issued it, and which establishment received it, exactly as they appear on the ภ.พ.20 (PP.20) VAT registration certificate: the words สำนักงานใหญ่ ('head office') or an abbreviation such as สนญ, HO, HQ, or the five zeros 00000; or สาขาที่ .. ('branch no. ..') with the branch number from the PP.20, or Branch No. .., br. no. .., or the five-digit branch code such as 00001. This applies to the issuer's address and, where the customer is VAT registered, to the customer's address too (Announcement No. 199, items 8 and 9).
- The VAT amount shown separately from the value of the goods or services, plus the serial number of the invoice (and of the invoice book if there is one), the description, type, quantity and value of what was supplied, and the date of issue (s.86/4).
Numbering, keeping and correcting invoices
Every tax invoice carries a serial number and, where invoice books are used, the book number (Revenue Code s.86/4(4)). Copies of tax invoices, reports and supporting documents are kept at the place of business for at least 5 years from the date the return was filed or the report made (s.87/3). After a registrant stops trading the records must still be kept for 2 more years, and the Director-General may order a longer period of up to 7 years.
When the value of a sale falls after the invoice (for example a return or a price cut), the seller issues a credit note in the tax month of the event, or in the following month if it could not be issued in time (s.86/10). The credit note carries the words "credit note" prominently, the original invoice serial number, the original value, the correct value, the difference, the VAT credited and a brief reason, and is treated as a tax invoice.
When the value rises, a debit note is issued on the same timing (s.86/9). Corrections are therefore made by credit or debit note, not by altering the original invoice.
Electronic invoicing in Thailand
Voluntary. Thailand has no e-invoicing mandate — no scheduled start date, no phased rollout, and nothing in the Revenue Department's published new-law list as at September 2026 that imposes one. The Revenue Department runs an opt-in system called e-Tax Invoice & e-Receipt (ใบกำกับภาษีอิเล็กทรอนิกส์และใบรับอิเล็กทรอนิกส์) at etax.rd.go.th: you apply for approval, sign each document with a digital certificate, deliver it to the customer electronically and send the data to the Revenue Department. A lighter route, 'e-Tax Invoice by Email', is run through the Revenue Department's time-stamp service at rd.go.th using application form ก.อ.09 (Kor.Or.09), and is aimed at smaller businesses. Both are optional, and an approved issuer is listed publicly at etax.rd.go.th/ETAXSEARCH/. Until you join one of them, an ordinary paper tax invoice meeting s.86/4 is correct and sufficient.