In which period should adjustment and replacement invoices be declared?

Kỳ kê khai phụ thuộc vào lý do lập hóa đơn điều chỉnh hoặc thay thế, không phụ thuộc ngày lập:

• Hóa đơn sai sót (sai thuế suất, đơn giá, số tiền, MST…): Người bán khai bổ sung vào kỳ của hóa đơn gốc. Người mua chỉ phải khai bổ sung kỳ gốc khi sai sót làm tăng thuế phải nộp hoặc giảm thuế được hoàn. Các trường hợp còn lại, người mua khai vào kỳ phát hiện hoặc kỳ nhận hóa đơn.
• Phát sinh sau giao dịch theo khoản 5 Điều 10 Thông tư 91/2026/TT-BTC (trả lại hàng, chiết khấu thương mại, điều chỉnh giá trị quyết toán…): Người bán khai vào kỳ lập hóa đơn điều chỉnh, người mua khai vào kỳ nhận. Không phải khai bổ sung kỳ gốc.

Quy định này áp dụng từ 01/7/2026, căn cứ Luật Quản lý thuế 2025, Điều 12 Nghị định 252/2026/NĐ-CP, khoản 6 Điều 23 Nghị định 181/2025/NĐ-CP và Điều 10 Thông tư 91/2026/TT-BTC. Phần dưới phân tích từng trường hợp, kèm 5 ví dụ kỳ cũ – kỳ mới.

Legal basis for determining in which period adjustment and replacement invoices should be declared, according to regulations.

Before delving into specific cases, accountants need to understand the entire legal framework upon which it will be applied, as this is a new system of regulations that will take effect simultaneously from July 1, 2026, and will replace many previous guidelines.

• The 2025 Tax Administration Law – General principles are stipulated in points a, b, and c of Clause 5, Article 12.
• Decree 252/2026/ND-CP – Detailed guidance in Article 12.
• Circular 89/2026/TT-BTC – Guidance on implementation related to tax declaration.
• Decree 181/2025/ND-CP – Document related to the management of invoices and supporting documents.
• Decree 254/2026/ND-CP – Regulations on electronic invoices and documents.
• Circular 91/2026/TT-BTC – particularly Article 10, specifies the process for handling erroneous electronic invoices.

The simultaneous application of multiple regulations often leads to confusion among accountants, especially in small and medium-sized enterprises. Therefore, to accurately answer the question of which period adjustment and replacement invoices should be declared, the first principle to understand is the nature of the adjustment or replacement and the declaration period, not the time the adjustment invoice is issued.

General principles for determining the filing period. 

According to the new regulations, there are two major groups of principles that need to be clearly distinguished:

Criteria	Due to an error	Due to issues arising after the transaction
Reason	Incorrect information on the issued invoice.	Returning goods, trade discounts, settlement, refunds or fee reductions, cancellation or termination of transactions.
Seller's declaration period	Original invoice period (supplementary declaration)	Adjustment billing period
Buyer's declaration period	Original invoice period (supplementary declaration)	Nếu làm tăng thuế phải nộp hoặc giảm thuế được hoàn, các trường hợp khác khai vào kỳ phát hiện hoặc nhận hóa đơn

The table above provides a general framework; the following section will analyze each case in detail so that accountants can accurately apply it to real-world situations within the business.

Reference: Invoices must be issued in accordance with Decree 254/2026/ND-CP.

Ví dụ về kỳ cũ và kỳ mới

Trường hợp sai thuế suất, thuế tăng: Hóa đơn tháng 7/2026. giá 100 triệu, ghi thuế suất 8% (8 triệu) thay vì 10% (10 triệu). Tháng 9/2026 phát hiện và lập hóa đơn điều chỉnh tăng 2 triệu tiền thuế.

• Người bán: Khai bổ sung tờ khai tháng 7/2026, nộp thêm 2 triệu và tiền chậm nộp tính từ sau hạn nộp của kỳ tháng 7.
• Người mua: Thuế đầu vào tăng, tức thuế phải nộp giảm, nên khai vào tháng 9/2026 (kỳ nhận), không khai bổ sung tháng 7.

Trường hợp sai đơn giá, điều chỉnh giảm: Hóa đơn tháng 7/2026 ghi thừa 20 triệu tiền hàng (thuế 10% là 2 triệu). Tháng 9/2026 lập hóa đơn điều chỉnh giảm.

• Người bán: Khải bổ sung tháng 7/2026, phát sinh số thuế nộp thừa.
• Người mua, trường hợp tháng 7 có thuế phải nộp: Thuế đầu vào giảm làm tăng số thuế phải nộp, nên khai bổ sung tháng 7/2026 và nộp tiền chậm nộp.
• Người mua, trường hợp tháng 7 vẫn còn thuế chuyển kỳ sau lớn hơn 2 triệu: Chỉ làm giảm số thuế chuyển kỳ sau, nên khai tại tháng 9/2026.

Trường hợp trả lại hàng, lập và nhận lệch tháng: Hóa đơn bán hàng tháng 7/2026. Khách trả một phần hàng, người bán lập hóa đơn điều chỉnh giảm ngày 28/9/2026, người mua nhận ngày 02/10/2026.

• Người bán: Khai vào tháng 9/2026
• Người mua: Khai vào tháng 10/2026, không khai bổ sung tháng 7. Theo Thông tư 89/2026, ngườ mua nhận hóa đơn thuộc khoản 5 Điều 10 Thông tư 91 thì khai vào chỉ tiêu [37] hoặc [38] của kỳ nhận hóa đơn, không phải khai bổ sung.

Trường hợp bỏ sót hóa đơn đầu vào: Hóa đơn mua vào tháng 7/2026 (thuế 5 triệu) chưa kê khai, đến tháng 9/2026 mới phát hiện. Kê khai bổ sung làm giảm thuế phải nộp, nên khai luôn vào tháng 9/2026, với đều kiện cơ quan thuế chưa công bố quyết định kiểm tra, thanh tra

Trường hợp chiết khấu thương mại qua mốc 01/7/2026, doanh nghiệp khai theo quý: Hóa đơn bán hàng theo Quý II/2026, chương trình chiết khấu theo doanh số kết thúc, hóa đơn điều chỉnh giảm lập ngày 15/7/2026. Hóa đơn điều chỉnh lập sau 01/7/2026 nên áp dụng quy định mới. Người bán khai Quý III/2026, người mua khai vào quý nhận hóa đơn.

In which period should adjustment and replacement invoices be declared when they arise due to errors?

The most common problem accountants encounter is an invoice containing errors, meaning the original invoice does not accurately reflect the nature of the transaction from the outset due to recording errors. This could include incorrect buyer's tax identification number, incorrect product name, incorrect amount, incorrect tax rate, or incorrect tax amount.

For this group of cases, the principle of declaration is uniformly stipulated that both the seller and the buyer must declare the adjustment in the tax period of the original invoice. In other words, even if the adjustment or replacement invoice is issued at the present time, the adjusted figures must still be returned to the tax period in which the original invoice was previously declared, through the form of supplementary declaration.

This approach helps ensure that the true nature of the transaction is reflected at the time it occurs, preventing the misuse of invoice adjustments to shift revenue, expenses, and taxes payable to a more advantageous period.

Exceptions to input invoices

Specifically for input invoices, the regulations have a notable flexibility that accountants need to pay particular attention to:

• If errors or omissions on input invoices only change the amount of deductible VAT carried forward to the next period, without increasing the tax payable or reducing the tax refund, the business is allowed to declare it immediately in the period in which the error is discovered (the current period), instead of having to go back to the original period.

This is a significant difference from the general principle, helping to reduce the burden of filing supplementary declarations for errors that do not affect the actual tax obligations of the business. However, accountants need to carefully assess the nature of the error before applying this exception, only applying it when the error does not affect the amount of tax payable or the amount of tax refundable; otherwise, the principle of filing supplementary declarations for the base period as mentioned above must still be followed.

In which period should adjustment and replacement invoices be declared when they arise after a transaction (not due to an error)?

Unlike errors, there are many situations where adjustment invoices are issued not because of initial recording errors, but because of events that occurred after the transaction was completed and the original invoice was correctly issued at that time. Typical situations include:

• Return goods that have been bought or sold.
• Trade discounts arise after the sale of goods.
• Contract settlement.
• Refund or reduce service fees.
• Cancel or terminate the transaction.

For this group of cases, the declaration principle is completely different from that for errors; there is no need to go back to the original period to make supplementary declarations, but each party declares independently according to the actual time of occurrence of their own case.

• The seller declares it in the adjustment invoice period.
• The buyer declares the adjusted invoice at the time of receipt.

It's important to note that the declaration periods of the seller and buyer in this case may not coincide, as the actual date of issuance and receipt of the adjusted invoice may differ.

 For example: The invoice is issued at the end of the month, but the buyer receives it at the beginning of the following month. 

This is why clearly distinguishing between errors and post-transaction issues is crucial in accurately answering the question of which period adjustment and replacement invoices should be declared in each specific business situation.

Procedure for handling erroneous output invoices according to Circular 91/2026/TT-BTC

After determining the declaration principles, the next step accountants need to master is the process of preparing adjustment invoices or replacement invoices in accordance with the regulations in Article 10 of Circular 91/2026/TT-BTC. This process applies generally to cases where output invoices contain errors and consists of the following four steps.

Step 1: Identify errors on the electronic invoice.

An issued electronic invoice is considered erroneous if it contains errors in the following areas: 

• Tax identification number;
• Product name;
• Specifications;
• The quality of goods stated on the invoice does not match the actual quality.
• The amount stated on the invoice; 
• Tax rate; 
• Tiền thuế hoặc các nội dung bắt buộc khác (trừ một số trường hợp riêng được quy định tại điểm a khoản 1 Điều 10 Thông tư 91/2026/TT-BTC).

Upon discovering these errors, the seller has the option of either issuing an adjusted invoice or issuing a replacement invoice for the incorrectly issued electronic invoice.

Step 2: Draft an agreement or notification to the buyer.

Depending on the buyer, the handling method will vary:

• If the buyer is an economic organization, other organization, household business, or individual business: Both parties must draw up a written agreement clearly stating the details of the error.
• If the buyer is an individual: The seller must notify the buyer, or make a public announcement on the seller's website (if available).

This agreement must be kept by the seller at their premises for presentation upon request by the tax authorities or other competent government agencies.

RemarkableThe regulations also specify several cases where a written agreement is not required, including: transferring electronic invoice data according to the Summary Table of Electronic Invoice Data as stipulated in point a.1, clause 3, Article 16 of Decree 254/2026/ND-CP; transferring detailed transaction information databases according to the Transaction Details Information Table as stipulated in point a.2, clause 3, Article 16 of Decree 254/2026/ND-CP; and the buying and selling of goods on e-commerce platforms and other digital platforms.

Step 3: Issue an adjustment invoice or replacement invoice.

When issuing an adjustment invoice or a replacement invoice, the new invoice must clearly state a reference to the original invoice:

For adjustment invoices: clearly state “Adjustment for invoice Form No… symbol… number… dated… month… year”.

For replacement invoices: clearly state “Replacement for Invoice Form No… Symbol… Number… Date… Month… Year”.

Providing complete and accurate reference information is crucial for tax authorities to verify, and also serves as the basis for accountants to correctly identify the original invoice when filing supplementary declarations (in case of errors) or declaring according to the period of issuance or receipt (in cases arising after the transaction). 

Step 4: Digitally sign and send the adjustment/replacement invoice.

The method of digitally signing and sending invoices depends on the type of electronic invoice the business is using:

• For electronic invoices without a tax authority code: The seller digitally signs the newly adjusted or replaced electronic invoice, then sends it directly to the buyer.
• For electronic invoices with a tax authority code: The seller digitally signs the new electronic invoice, then sends it to the tax authority to obtain a code, before sending it to the buyer.

In addition, the regulations allow for a convenient consolidation mechanism for businesses with large transaction volumes:

• In cases where, within a month, the seller has incorrectly issued multiple invoices to the same buyer containing the same information regarding the buyer, product name, unit price, quantity, and tax rate, the seller may issue a single adjustment or replacement invoice for all the incorrect invoices, accompanied by a list of the incorrectly issued electronic invoices using Form No. 01/BK-ĐCTT in Appendix III. Circular 91/2026/TT-BTC. 

Important notes to avoid incorrectly declaring adjustment and replacement invoices. 

To minimize risks when handling situations related to invoice adjustments and replacements, accountants should establish an internal control process following these steps:

• First, determine the true nature of the issue: Does this adjustment or replacement invoice stem from an information error, or from an event occurring after the transaction (return of goods, discount, contract cancellation, etc.)? This step will determine how the declaration process will proceed.
• If it is an error, the supplementary declaration will be automatically included in the original invoice period, except for exceptions for input invoices that do not increase the tax payable or decrease the tax refund, in which case it can be declared in the period in which the error is discovered.
• If the adjustment occurs after the transaction, the seller and buyer declare it independently: the seller declares it according to the period in which the adjustment invoice was issued, and the buyer declares it according to the period in which the adjustment invoice was received; there is no need to go back to the original period.
• Always prepare all necessary written agreements or notifications to the buyer as required in Step 2 of the erroneous invoice handling process, as legal basis for storage and presentation when needed.
• Review and submit supplementary tax returns on time to avoid late payment penalties or administrative tax violation fines when the tax authorities conduct audits or inspections.

Understanding this process not only helps accountants accurately answer the question of which period adjustment and replacement invoices should be declared in each specific transaction, but also contributes to minimizing legal risks for businesses in the context of continuously updated regulations on electronic invoices and documents. 

For small and medium-sized enterprises, the use of full accounting service This is a solution that helps ensure all transactions related to adjustment and replacement invoices are processed and declared correctly and in accordance with regulations from the outset, minimizing the risk of being subject to back taxes or penalties during final settlement. 

Conclude

In summary, to accurately answer the question of which period adjustment and replacement invoices should be declared in, accountants need to adhere to two core principles: 

• If there is an error, declare it in the original invoice period (except for input invoices that do not affect the amount of tax payable/refundable); 
• If the adjustment arises after the transaction, such as returns, discounts, or contract cancellations, each party must declare it independently according to the period in which the adjustment invoice was issued or received.

Simultaneously, adhering to the correct 4-step process for issuing adjustment/replacement invoices as stipulated in Circular 91/2026/TT-BTC will help businesses ensure compliance with the law while minimizing risks during tax settlement and audits. With the new regulations officially effective from July 1, 2026, accountants should proactively update and review their procedures. Handling erroneous invoices at your company as soon as possible.

If a business does not yet have a sufficiently strong dedicated accounting department to closely monitor these new regulations, the solution is... hire an external accountant This will help ensure that the period for which adjustment and replacement invoices are declared is always accurate and timely, while also significantly saving operating costs compared to maintaining an in-house accounting department. 

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Responsible for production and professional content review by: Mr. Le Hoang Tuyen – Founder & CEO of MAN – Master Accountant NetworkHe is a CPA Vietnam auditor with over 30 years of in-depth experience in accounting, auditing, taxation, and corporate legal consulting.

Answering questions about which period adjustment and replacement invoices should be declared. 

Hóa đơn sai thông tin người mua thì kê khai kỳ nào?

Nếu chỉ sai tên hoặc địa chỉ nhưng đúng mã số thuế: thường không phải lập hóa đơn điều chỉnh/thay thế mà chỉ thông báo cho người mua (đối chiếu điểm a khoản 1 Điều 10 Thông tư 91/2026), nên không phát sinh kê khai lại. Nếu sai mã số thuế: phải lập hóa đơn điều chỉnh hoặc thay thế. Số thuế không đổi nên thường không phát sinh số thuế khai bổ sung; người mua kê khai hóa đơn đúng vào kỳ nhận.

In which period should adjusted invoices resulting from returned goods be declared?

This is a case of an event occurring after the transaction, not an error. The seller declares it in the period the adjustment invoice is issued; the buyer declares it in the period the adjustment invoice is received.

Is it mandatory to re-declare the original invoice if there are errors?

Chỉ bắt buộc khi sai sót làm tăng thuế phải nộp hoặc giảm thuế được hoàn của kỳ gốc. Nếu sai sót làm giảm thuế phải nộp, hoặc chỉ làm thay đổi số thuế còn được khấu trừ chuyển kỳ sau, doanh nghiệp khai vào kỳ phát hiện. Điều kiện chung là phải khai trước khi cơ quan thuế công bố quyết định kiểm tra, thanh tra (khoản 6 Điều 23 Nghị định 181/2025).

When do the regulations regarding the reporting period for adjusted and replacement invoices come into effect?

Từ 01/7/2026, theo Luật Quản lý thuế 2025, Nghị định 252/2026, Nghị định 254/2026, Thông tư 89/2026 và Thông tư 91/2026. Riêng Nghị định 181/2025 về thuế GTGT đã áp dụng từ 01/7/2025. Hóa đơn điều chỉnh lập trước 01/7/2026 xử lý theo Nghị định 70/2025.