What every invoice must show
- The four entries the Act calls 필요적 기재사항: the supplier's registration number and name, the recipient's registration number, the value of supply and the VAT, and the date of preparation. Any one missing or wrong costs 1% of the value of supply, charged to both parties.
- 공급가액 and 세액 as separate figures. A Korean tax invoice does not show one gross total and leave the reader to work the tax out.
- The buyer's registration number, which means checking their number and status on Hometax before you issue. For a buyer who is not a business, their resident registration number goes there instead.
- The right form: a tax-exempt sale goes on a 계산서, not a 세금계산서 — same system, no VAT line.
Numbering, keeping and correcting invoices
An entrepreneur must record every transaction affecting tax payable or refundable in account books and keep them at the place of business (VAT Act Art. 71(1)). A business that sells both taxable and exempt goods must enter the two separately (Art. 71(2)).
Books, plus the tax invoices, import tax invoices and receipts issued or received, must be preserved for five years from the final-return deadline of the taxable period to which the transactions belong (Art. 71(3)). The duty to keep the invoice itself falls away for an electronic tax invoice whose list has been transmitted to the NTS Commissioner.
Errors are corrected by issuing a corrected tax invoice, not by altering the original (Art. 32(7)).
Electronic invoicing in South Korea
Mandatory, and long established. Every company has had to issue electronic tax invoices since January 2011, and NTS has walked the threshold for individual businesses down from KRW 1 billion in 2012 to KRW 80 million from July 2024, which is the figure today. It is measured per place of business on the previous year's taxable and tax-exempt supplies together, and the duty starts in the second tax period of the following year — KRW 80 million of 2025 supplies puts you in from 1 July 2026 — and stays once triggered, even if turnover falls back. Issue free on Hometax or the Sontax app, through an NTS-registered ASP or your own ERP, or by phone on 126 with a security card from the tax office. Two deadlines, not one: issue by the 10th of the month after the supply, and transmit to NTS by the day after issuing. Issuing late but within the return deadline costs 1% of the value of supply, never issuing 2%, issuing on paper when you were obliged to issue electronically 1%; transmitting late 0.3% and never transmitting 0.5%. June and December supplies have no room between the 10th and the return deadline, so a late one there goes straight to 2%. An individual general taxpayer gets a credit of KRW 200 an invoice, capped at KRW 1 million a year. From 1 January 2026 the penalty for a wholly fabricated invoice rose from 3% to 4%.