Debit & Credit Notes for Fuel Stations — When & How

You issue a bill, the total turns out wrong, and money has to be added or reduced afterwards — a normal part of life for stations selling on credit, especially when fuel prices are revised retroactively under the parent oil company's announcement. Many stations fix it the risky way, reprinting a bill over the old one or editing the figures in Excel, which has consequences for both tax and audits. This article summarizes when to use a debit note, a credit note, and a reissued bill — and how to do each one correctly.

There is only one principle to remember: a document that has already been issued is history and must be kept as it is. Every upward or downward adjustment is made with a separate document that references the original — nothing overprinted, nothing deleted, nothing torn up. Once that principle holds, every case below falls into order, and the accounting team no longer wastes the end of the year chasing documents that vanished.

When to use a debit note

A debit note (ใบเพิ่มหนี้) is used when the amount from the original tax invoice has to go up. Cases a station meets often: the price was keyed below the announced price at the time; charges were added after billing, such as delivery or special service fees; or the bill was issued for less than the quantity actually delivered. The debit note is a separate document referencing the original invoice number, stating the amount added and a clear reason. In accounting terms, the sales and VAT of the period in which it is issued rise accordingly — which keeps the station from selling at a loss without noticing.

When to use a credit note

A credit note (ใบลดหนี้) is used when the amount has to come down: the price was above what was agreed, a discount was given after billing, the customer returned goods, or the total was overstated. In accounting terms, the sales and VAT of the period in which the credit note is issued fall accordingly. Stations reach for credit notes more often during fuel price cuts — but do not neglect the other side, because raising amounts correctly with a debit note matters just as much. The two documents are opposite halves that have to work as a pair all year.

3 rules every debit note and credit note must follow

1. Reference the original tax invoice every time. State the number and date of the source invoice, so it is clear which document the adjustment belongs to.
2. State the reason for the increase or decrease clearly — for example, a retroactive price revision following the diesel B7 price announcement for the cycle of the 15th.
3. Record it in the books and file the tax in the period the document was issued, not the period of the original transaction, because the sales tax filing must match the documents actually issued in each period.

All three rules can be checked from document numbers and tax periods alone, so they are the first thing an auditor will see. The basics of issuing tax invoices correctly from the start are in Receipts and tax invoices for fuel stations.

When a credit customer asks for a copy: how to do it right

Corporate customers losing documents several times a year is normal. What is forbidden is reprinting the bill as another original, because that would leave two identical tax documents in circulation — something that should never happen in accounting or in law. The correct way is to print a true copy from the system, clearly marked as a copy, keeping the original number and issue date; the original itself stays the same sheet on file. A good system has a print-copy button that stamps the word copy automatically and logs who printed it and when, so you can trace where the document went at any time.

The case stations meet most: retroactive price revisions from the parent company

When the parent company announces a retroactive price revision — diesel B7 down 0.40 baht per liter, back to the 15th of the previous month, for example — a station that has already billed its credit customers must adjust the whole cycle. The correct way is to issue a credit note or debit note per receivable account, following the revision cycle, citing the price announcement as the reason on the documents. A station billing through a system can generate this set of documents in a few clicks, because the system knows which bill used which price window. A station doing it by hand spends days on it and can easily get it wrong every cycle.

Document numbering discipline: sequential, never skipping

Every kind of tax document must run in one unbroken sequence within the year. Debit notes and credit notes have their own series, separate from regular tax invoices. A skipped or duplicated number must have a document explaining it. The safest approach is to let the software assign the numbers itself: a document printed with a wrong number still stays in the sequence, and a cancelled bill is kept in the book, so every number can be traced afterwards. This is exactly where a fuel station POS system solves what manual numbering never can, because small mistakes accumulate over the year into a document file full of floating gaps.

How this ties into billing your receivables

Debit notes and credit notes are one piece of the receivables billing process. Once the amounts have been adjusted with the correct documents, the next cycle's reconciliation statement picks up the new totals immediately — no ambiguous leftover balances to negotiate, and no calls from customers asking why the totals do not match. The whole chain runs more smoothly end to end. The full billing cycle is covered in Billing fuel station receivables: reconciliation statements that collect on time

Documents that add or subtract money are not hard — they just demand the same discipline every time: reference the original document, state the reason, assign numbers in sequence, and file the tax in the period of issue. A station that runs this as a system keeps many times more time for selling than for fixing paperwork. If you want to see how a system handles this whole document set, message us for a consultation any day — free, with no commitment.