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Value Added Tax (VAT)

Amending a VAT Return in Vietnam 2026: When to Use Indicator [37]/[38] vs. When a Supplementary Filing (KHBS) Is Required

By TrustlineAX Advisory August 14, 2026 9 min read

Amending a VAT Return in Vietnam 2026: When to Use Indicator [37]/[38] vs. When a Supplementary Filing (KHBS) Is Required

One of the most common questions accountants face when preparing a VAT return is: if an error is discovered or prior-period figures need adjusting, does it require a supplementary tax return (KHBS), or is it enough to fill in indicator [37] or [38] on the current return? From 1 July 2026, this issue is governed afresh by the Law on Tax Administration No. 108/2025/QH15, Decree No. 252/2026/ND-CP, and Circular No. 89/2026/TT-BTC (Form 01/GTGT). This article, prepared by TrustlineAX, distinguishes the two adjustment mechanisms, lists the specific cases each applies to, and provides worked examples.

1. Two mechanisms for adjusting a VAT return

In substance, there are two ways to handle a correction to a prior period’s VAT figures:

  • Method 1 — Direct adjustment in the current period via indicator [37] or [38] on Form 01/GTGT, without filing a supplementary return.
  • Method 2 — Filing a supplementary tax return (Form 01/KHBS) for the exact tax period containing the error, under Article 12 of Decree No. 252/2026/ND-CP (implementing Clause 5, Article 12 of the Law on Tax Administration No. 108/2025/QH15).

Choosing the correct method depends on the nature of the adjustment: where it only affects the input VAT still creditable to future periods (without increasing the tax payable of a past period), Method 1 typically applies; where the error changes the tax payable, or the amount already exempted, reduced, or refunded for a prior period, Method 2 must be used.

2. What are indicators [37] and [38] on Form 01/GTGT?

Under the notes accompanying Form 01/GTGT issued with Circular No. 89/2026/TT-BTC:

  • Indicator [37]: used to decrease the input VAT still creditable from prior periods.
  • Indicator [38]: used to increase the input VAT still creditable from prior periods.

An important note: these two indicators are used only to adjust input VAT (still creditable) up or down — they are not used to adjust output VAT.

Cases eligible for direct declaration via indicator [37]/[38] (no supplementary return required)

a) Goods or services purchased on deferred or installment payment terms of VND 5 million or more, where non-cash payment documentation is not yet available by the due date. Under Article 4 of Decree No. 144/2026/ND-CP (amending Point g, Clause 2, Article 26 of Decree No. 181/2025/ND-CP): once the contractual payment due date has passed without non-cash payment documentation, the business must self-adjust to decrease the corresponding input VAT for the unpaid, non-cash portion (recorded in indicator [37] of the period the payment obligation arises); once non-cash payment documentation is later obtained, the amount may be adjusted back upward (recorded in indicator [38] of the period the documentation is obtained).

b) An input VAT error discovered within the same period it arose (before finalization, before any tax inspection), where the adjustment only increases or decreases the tax still creditable to future periods (without increasing the tax payable of the period containing the error), is declared in indicator [37] or [38] of the month or quarter in which the error is discovered — no supplementary return is required.

c) Receiving an adjustment invoice or a replacement invoice falling within the cases prescribed under Clause 5, Article 10 of Circular No. 91/2026/TT-BTC (for example: adjusting the settlement value of an investment project, adjusting wholesale electricity prices, volume-based trade discounts, returned goods, insurance premium refunds, etc.). The buyer declares this in indicator [37]/[38] of the period the adjustment or replacement invoice is received (the seller declares it in the period the adjustment invoice is issued).

d) Switching the tax calculation method from the credit method to the direct-on-revenue method: any unclaimed input VAT is adjusted down via indicator [37] in the final tax period before the switch (under Clause 11, Article 23 of Decree No. 181/2025/ND-CP).

e) Implementing a conclusion or handling decision from the tax authority or a competent authority that increases or decreases the VAT still creditable to future periods (including a refund-denial notice): declared in indicator [37]/[38] of the period the conclusion, decision, or notice is received — no supplementary return required.

3. When is a supplementary tax return (01/KHBS) mandatory?

Under Clause 5, Article 12 of the Law on Tax Administration No. 108/2025/QH15 and Article 12 of Decree No. 252/2026/ND-CP, a taxpayer who discovers an error in an already-filed tax return may file a supplementary return within 5 years from the filing deadline of the tax period containing the error, provided the case falls within the eligible scope: before an inspection or examination decision is issued; the return is outside the scope/period already inspected or examined; the return is not subject to a request from an investigating authority to suspend supplementary filing; and so on.

As a matter of principle, a supplementary return applies to the tax period in which the error actually occurred (as distinct from indicator [37]/[38], which adjusts the current period / the period of discovery). Under Appendix II issued with Circular No. 89/2026/TT-BTC, the specific handling is as follows:

  • An error that only increases the unclaimed input VAT carried to future periods: file a supplementary return for the period containing the error; the increase is declared in the indicator “Increase in VAT still creditable from prior periods” on that supplementary return itself.
  • An error that decreases the unclaimed input VAT carried to future periods (no refund yet requested): similarly, file a supplementary return for the period containing the error, with the decrease recorded directly on that supplementary return.
  • An error that both decreases creditable VAT and increases the tax payable for the period containing the error: the business must pay the additional tax payable plus any late-payment interest to the state budget.
  • Where a refund request has already been filed for the period containing the error, whether or not yet refunded (including pre-refund cases): a written request to cancel/withdraw the corresponding refund dossier must be submitted, together with the supplementary filing.
  • An error affecting both Form 01/GTGT and Form 02/GTGT simultaneously (relating to an investment project): supplementary filings must be made consistently across both forms.

The key point: the result of the supplementary return (KHBS) flows back into indicator [37]/[38] of the current period

This is the point most likely to cause confusion: after completing a supplementary return (Form 01/KHBS) for the period containing the error, the result at indicator 12, Section II of that supplementary return (the difference in creditable VAT compared to what was originally declared) is then carried forward into indicator [37] or [38] of the current period’s return (the period in which the supplementary filing is actually made) — it does not stop at the supplementary return itself:

  • If indicator 12 on the supplementary return is positive: that amount is carried into indicator [38] of the current period (an upward adjustment).
  • If indicator 12 on the supplementary return is negative: that amount is carried into indicator [37] of the current period (a downward adjustment).

In other words, filing a supplementary return and adjusting via indicator [37]/[38] are not mutually exclusive — in many cases both steps are required: filing a supplementary return for the period containing the error (to re-establish that period’s tax liability), and separately reflecting the resulting difference in creditable VAT on the current period’s return.

4. Worked examples

Example 1 — Adjusting indicator [37] for goods purchased on deferred terms, not yet paid by non-cash means:

On 15 June 2026, Company A purchases equipment from Company B valued at VND 100,000,000, with 8% VAT of VND 8,000,000, for a total payment of VND 108,000,000, under a deferred-payment contract due no later than 15 July 2026. Company B issues a valid VAT invoice on 15 June 2026.

  • For the Q2 2026 period (return filed 10 July 2026): since the payment due date has not yet passed, Company A may credit the VND 8,000,000 input VAT normally, based on the contract and invoice.
  • By 15 July 2026 (falling in Q3 2026), Company A still has not paid Company B and has no non-cash payment documentation → Company A must adjust down by VND 8,000,000 via indicator [37] on the Q3 2026 return.
  • Assume that by 10 October 2026 (Q4 2026), Company A pays by bank transfer → the VND 8,000,000 is adjusted back up via indicator [38] on the Q4 2026 return.

Example 2 — An error that only affects creditable VAT, no supplementary return needed:

In the August 2026 period, Company C’s accountant discovers that an input invoice from August 2026 (the current period, return not yet filed) was omitted, with VAT of VND 3,000,000, which only increases the VAT still creditable to future periods (the company has a credit balance and no tax payable for the period). Because it was discovered and declared within the same period it arose, and does not reduce the tax payable of any other period, the accountant simply includes VND 3,000,000 in indicator [38] of the August 2026 return — no supplementary return is needed.

Example 3 — A supplementary return (KHBS) is required because the error belongs to an already-filed prior period:

In September 2026, Company D’s accountant discovers that the Q1 2026 return (already filed) understated creditable input VAT by VND 5,000,000 (due to an omitted valid invoice arising in Q1 2026), causing the VAT creditable to future periods for Q1 2026 to be understated.

  • Step 1: Company D files a supplementary return (01/KHBS) for the Q1 2026 period, correctly reflecting the additional VND 5,000,000 of creditable VAT for that period.
  • Step 2: The result at indicator 12, Section II of this supplementary return is positive (+VND 5,000,000) → Company D carries this VND 5,000,000 into indicator [38] of the Q3 2026 return — the current period, the period in which the supplementary filing is actually made (not the Q1 2026 period containing the error).

5. Key points for accountants

  • Always determine clearly whether the error changes the tax payable, or the amount already exempted, reduced, or refunded for a prior period — this is the most important line distinguishing a simple indicator [37]/[38] adjustment from a mandatory supplementary filing.
  • Where a supplementary filing increases the tax payable or reduces an amount already exempted, reduced, or refunded, the business must pay the full additional amount and any late-payment interest (if applicable) to the state budget.
  • Where a refund request has already been filed for the period containing the error, the corresponding refund dossier must be cancelled or adjusted before or together with the supplementary filing, per Circular No. 89/2026/TT-BTC.
  • Businesses with investment projects (declared separately on Form 02/GTGT) should pay particular attention to supplementary filings that affect both Form 01/GTGT and Form 02/GTGT together, to avoid data mismatches.
  • Businesses should retain complete supporting documentation (contracts, invoices, payment records, tax authority conclusions/decisions if any, etc.) as the basis for each adjustment, to support explanations if requested by the tax authority.

This article was prepared by TrustlineAX based on the Law on Tax Administration No. 108/2025/QH15 (Article 12), Decree No. 252/2026/ND-CP (Article 12), Circular No. 89/2026/TT-BTC (Form 01/GTGT and Appendix II — Method for Filing a Supplementary Tax Return), Circular No. 91/2026/TT-BTC (Article 10), Decree No. 144/2026/ND-CP, and Decree No. 181/2025/ND-CP. The worked examples illustrate general principles only and do not replace the original legal texts or specialized tax advice for individual circumstances.