Taxpayer With Two Personal Tax Codes: Does a Dependent Deduction Still Count If Registered Under a Different Code?
RegHub explainer by New MarketerLast updated:
Based on:90/2026/TT-BTC - Ministry of Finance
This explanation was generated by AI and checked by an automated AI review, not by a human expert. It is not legal, tax or accounting advice and may contain errors. Check the official document before you rely on it.
An employee discovered she had unknowingly been issued two personal tax codes (MST), with no clear reason for the duplication. When her company finalized her personal income tax (PIT), her two registered dependents (NPT) turned out to be linked to the second tax code, while the finalization itself was processed under the first tax code. She was concerned this might disqualify her from the family circumstance (dependent) deduction for those two dependents. Responding, the Thai Nguyen Provincial Tax Department cited Clause 4, Article 37 of Circular No. 90/2026/TT-BTC dated 30 June 2026 issued by the Ministry of Finance on tax registration: an individual who has been issued more than one tax code must update the personal identification number information for all tax codes issued, so the tax authority can consolidate the codes under that personal ID number and unify the taxpayer's tax data accordingly. Once the tax codes are merged, invoices, documents, and tax records previously issued using any of those tax codes remain valid for tax administrative procedures and for proving fulfillment of tax obligations, without needing to be reissued under the personal ID number. In other words, once the two tax codes are consolidated under the same personal identification number, dependent information declared under the second tax code is still recognized as belonging to the same employee. The tax authority also referenced Official Letter No. 3422/CT-NVT dated 27 May 2026 from the Tax Department (with Appendix 01), which provides detailed instructions on how to check tax code status and update personal identification numbers, and advised the taxpayer to follow that guidance to ensure the dependent deduction is not affected.
The Question
Ms. Dao Thi Mai reported that her company has an employee who was issued two personal tax codes (MST), for reasons the employee herself does not know. When the company processed her personal income tax (PIT) finalization through the income-paying organization, the finalization dossier - filed under the first tax code - declared 2 dependents (NPT), but in the tax system those two dependents were actually linked to the second tax code. In substance, this is still a single employee; only the dependent records happen to sit under a different tax code. Ms. Mai asked: are dependents declared during PIT finalization under the first tax code (not the second) still eligible for the family circumstance (dependent) deduction?
The Answer
The Thai Nguyen Provincial Tax Department responded by citing Clause 4, Article 37 of Circular No. 90/2026/TT-BTC dated 30 June 2026 issued by the Ministry of Finance on tax registration, which sets out the following transitional provision:
«4. Where an individual has been issued more than one (1) tax code, the taxpayer must update the personal identification number information for all tax codes issued, so that the tax authority can consolidate those tax codes under the personal identification number and unify the taxpayer's tax data accordingly.
Once a tax code has been consolidated under the personal identification number, invoices, documents, tax records, and other legally valid papers previously issued using that individual's tax code information may continue to be used for tax administrative procedures and to prove fulfillment of tax obligations, without needing to have the tax code information on those invoices, documents, or tax records adjusted to the personal identification number.»
The tax authority also cited Official Letter No. 3422/CT-NVT dated 27 May 2026 issued by the Tax Department (in Appendix 01) regarding individuals issued multiple tax codes and updating personal identification numbers. That official letter provides detailed instructions on how to check a tax code's status and update the personal identification number.
What Taxpayers Should Do
The Thai Nguyen Provincial Tax Department advised the taxpayer to review Official Letter No. 3422/CT-NVT and follow its guidance, specifically:
- Update the personal identification number (citizen ID) information for both tax codes that were issued.
- Once the tax authority consolidates the two tax codes under the same personal identification number, all tax data - including dependent information registered under the second tax code - will be merged and recorded jointly under that taxpayer.
- Records and documents already filed (including the PIT finalization dossier that declared dependents under the first tax code) remain valid and do not need to be re-adjusted to the personal identification number.
Note: The official reply does not give a direct 'yes' or 'no' to the dependent-deduction question. Instead, it directs the taxpayer to consolidate the tax codes under one personal identification number - once merged, the dependent data is recognized jointly, regardless of which of the two tax codes was originally used to register it.