Vietnam CIT finalisation for 2026: a Q4 roadmap to avoid tax reassessments

The short answer

For companies with a calendar financial year, the deadline to file the 2026 CIT finalisation return and pay any balance is 31 March 2027. In practice, however, the outcome is decided in Q4 2026.

Two provisional payment deadlines remain:

• Q3 2026: due 31 October 2026. This falls on a Saturday, so the deadline moves to Monday, 2 November 2026.

• Q4 2026: due 31 January 2027. This falls on a Sunday, so the deadline moves to Monday, 1 February 2027.

Under Decree No. 252/2026/ND-CP, provisional payments for the four quarters must total at least 80% of the finalised CIT liability. Any shortfall attracts late-payment interest of 0.03% per day.

Why 2026 calls for earlier preparation

2026 is the first finalisation cycle shaped by several new instruments at once:

• the 2025 CIT Law and Decree No. 320/2025/ND-CP, applying for the full year;

• the 2025 Law on Tax Administration and Decree No. 252/2026/ND-CP, in force from 1 July 2026;

• Decree No. 254/2026/ND-CP on e-invoices;

• Decree No. 255/2026/ND-CP on related-party transactions.

Expenses that were deductible in 2024 may now be disallowed. Invoice timing is stricter. The tax authority also prioritises remote audits on electronic data.

If the review waits until March 2027, there is little room left to adjust. Q4 is the window to fix processes, complete documentation and set the right provisional payment.

Six-month roadmap: October 2026 to March 2027

Timing	Action	Purpose
October 2026	Estimate full-year taxable profit. Pay the Q3 provisional amount by 2 November 2026	Avoid back-loading the liability into Q4
November 2026	Review deductible expenses under Decree 320/2025. Filter invoices of VND 5 million or more not paid via bank	Fix issues while still within the financial year
December 2026	Stock count and write-off files for obsolete inventory. FX revaluation. Finalise related-party documentation	Ensure documentation is complete before closing
January 2027	Close the books and calculate the expected tax. Pay the Q4 provisional amount by 1 February 2027, meeting the 80% threshold	Avoid interest on any shortfall
February 2027	Three-way reconciliation of e-invoices, ledgers and tax returns. Complete financial statements and incentive files	Reduce risk when the authority matches data
March 2027	File the finalisation return and pay any balance by 31 March 2027	Finish on time

7 technical points most likely to trigger reassessments

1. The 80% provisional payment rule. Each quarter's provisional payment is self-determined. The condition is that the four quarters together must reach at least 80% of the finalised tax. Any shortfall carries late-payment interest from the day after the Q4 provisional deadline.

Note also that late quarterly payments may attract interest separately for each quarter.

2. Disallowed expenses under Decree 320/2025. The items most often disallowed are:

• invoices of VND 5 million or more paid in cash;

• interest on loans from non-credit institutions above the Civil Code cap;

• overtime pay beyond the limits of labour law;

• voluntary pension and life insurance above VND 5 million per person per month.

3. Revenue recognised out of line with invoice timing. From 1 July 2026, the invoicing-time rules under Decree 254/2026 are matched automatically by the tax authority. Gaps between accounting revenue, VAT-return revenue and CIT-return revenue are among the first risk flags the system raises.

4. Eligibility for the 15% and 17% rates. Companies with revenue up to VND 3 billion qualify for 15%; those with VND 3–50 billion qualify for 17%. These rates do not apply, however, where the company is a subsidiary or related party of an enterprise that does not itself qualify. Re-test eligibility before the Q4 provisional payment.

5. Related-party transactions. Decree 255/2026 applies from the 2026 tax year and raises the transfer pricing documentation exemption threshold to revenue below VND 500 billion. Related-party disclosure obligations and interest deduction limits still apply.

6. Incentives and loss carry-forward. Businesses self-assess incentive eligibility and the losses carried forward. Supporting files should therefore be ready at finalisation, not assembled only when an audit begins.

7. Errors in prior years. The 2025 Law on Tax Administration cuts the amendment window to 5 years. This finalisation is a good moment to review and self-amend earlier periods whose window is about to close.

Illustrative case

Company C estimates its 2026 CIT at VND 1.2 billion and has paid VND 500 million provisionally for Q1–Q3. To reach the 80% threshold (VND 960 million), it pays a further VND 460 million for Q4 by 1 February 2027.

During the finalisation review in March 2027, it discovered several disallowed expenses. Finalised tax rises to VND 1.5 billion, so the 80% threshold is now VND 1.2 billion. The provisional payments therefore fall VND 240 million short.

If the shortfall is paid on 31 March 2027, the estimated late-payment interest is:

• VND 240,000,000 × 0.03% × 58 days ≈ VND 4.18 million.

The amount is modest. The real problem is that the disallowed expenses were found too late. A review in November 2026 would have allowed the company to fix its policies, complete its documents and pay provisional tax close to the actual figure.

Pre-filing checklist

1. Reconcile revenue across e-invoices, ledgers, VAT returns and the CIT return.

2. Prepare a schedule of non-deductible expenses with the legal basis for each item.

3. Check eligibility for preferential rates, exemptions, reductions and loss carry-forward.

4. Complete the related-party disclosure appendix and transfer pricing documentation where required.

5. Compare provisional payments against the 80% threshold and calculate any late-payment interest.

6. Review foreign contractor tax withheld during the year, especially on service fees, royalties and software.

7. Keep all files in electronic form, ready for a remote audit.

FAQs

When is the 2026 CIT finalisation deadline?

For a calendar financial year, the return must be filed and any balance paid by 31 March 2027.

When is the Q4 2026 provisional CIT payment due?

Under Decree No. 252/2026/ND-CP, it is due on the last day of the first month of the following quarter, i.e. 31 January 2027. As this is a Sunday, the deadline moves to 1 February 2027.

Is there a penalty for paying less than 80%?

There is no administrative fine for this alone. However, the shortfall against the 80% threshold attracts late-payment interest at 0.03% per day.

Must a quarterly provisional CIT return be filed?

No. Businesses determine and pay the quarterly provisional amount without filing a quarterly return.

Legal basis

• Law on Tax Administration No. 108/2025/QH15.

• Decree No. 252/2026/ND-CP guiding the Law on Tax Administration (Article 24 on quarterly provisional payments).

• CIT Law No. 67/2025/QH15 and Decree No. 320/2025/ND-CP.

• Decree No. 254/2026/ND-CP on invoices and e-documents.

• Decree No. 255/2026/ND-CP on tax administration of related-party transactions.

How W&A can help

A safe finalisation is decided in Q4, not in the last week of March. W&A supports businesses throughout the cycle:

• Pre-closing tax review: identifying expenses at risk of disallowance and revenue or invoicing risks while there is still time to act.

• Q4 provisional payment planning: meeting the 80% threshold without overpaying or tying up cash.

• CIT and PIT finalisation filings, including related-party appendices and incentive documentation.

• Prior-year tax health checks: identifying periods to amend within the 5-year window.

• Support with explanations when the tax authority reviews the finalisation.