An employer can declare one salary level to the tax authority and contribute insurance on a lower one for years without being asked — until the two agencies’ data are cross-matched. When a joint inspection points to the gap between total wages in the personal income tax finalisation and the social insurance contribution payroll, the employer must explain it item by item. This article analyses the matching mechanism, the gaps that are legitimately explainable, and the consequences of the part that cannot be explained.
How insurance and tax data are cross-matched
The social insurance agency and the tax authority share and reconcile labour and wage data under an inter-agency coordination mechanism: employee lists, total paid payroll and each individual’s taxable income from the tax side are matched against the insured employee list and contribution salary bases from the insurance side. Large, persistent, system-wide gaps are the signal that selects an employer for thematic inspection plans on social insurance contribution.
What employers must understand is that the two bases are not identical by design: the insurance base is contractual salary comprising the wage rate, salary allowances and determinable supplements, while tax-finalised income also includes items outside the contribution base such as certain support and welfare amounts as prescribed. Every gap therefore has a legitimate component — the employer’s task in an inspection is to quantify that component with documents, so the remainder is not presumed wholesale to be contribution evasion.
Explainable gaps and unexplainable gaps
Explainable items include: income outside the salary components forming the social insurance contribution base as prescribed, such as in-limit mid-shift meal money and welfare-type support not recorded as fixed contractual supplements; income of employees outside compulsory coverage, such as rehired retirees and foreign employees in periods where they fall outside the applicable scope; and timing differences because the tax finalisation period and the contribution period do not coincide perfectly.
The unexplainable group is actual pay to compulsorily covered employees on which the employer systematically contributed at a lower contract salary — usually exposed when internal payrolls, bank salary payment data and tax finalisation all point to income well above the contribution base. For this group, the employer is back-assessed insurance on the gap for the entire period the practice ran, with late amounts of 0.03% per day under Article 40 of the Social Insurance Law 41/2024/QH15 and administrative sanctions scaled to the violation.
Working with the inspection team and the long-term fix
On receiving an inspection notice, the first step is self-reconciling three data sources — payroll and salary payment documents, personal income tax finalisation, and insurance contribution registration — per person and per period, building a structured gap-explanation table: total income per tax records, minus documented non-base items, minus non-covered groups, leaving the substantive gap to be dealt with. Presenting that table proactively lets the employer control the inspection’s narrative instead of answering question by question on the back foot.
Long term, the root of the gap is two parallel salary systems: a low contract payroll for insurance and higher real income through side items. The durable fix is base unification: adjusting contracts and salary scales so the contribution base correctly reflects the statutory salary components, and placing genuinely additional support into the lawful non-base categories instead of disguising salary as support. The compliance cost increase is real, but far smaller than one comprehensive back-assessment with fines and an inspection expanded into other fields.
Frequently Asked Questions
What happens when a joint inspection finds gaps between SI wages and PIT filings?
The employer must explain the gap item by item. Documented portions belonging to non-contribution-base income or non-covered employees are accepted. Actual pay to covered employees contributed at a lower base is back-assessed for the whole period, with 0.03%-per-day late amounts and administrative sanctions.
Which income items are outside the SI contribution base and thus explainable?
Items outside the salary components forming the contribution base as prescribed, such as in-limit mid-shift meal money and welfare support not constituting determinable contractual supplements. Income of employees outside compulsory coverage, such as rehired retirees, is likewise not contributable. Every explained item needs documents and corresponding contract grounds.
What should an employer prepare before a joint inspection works?
Self-reconcile three sources per person and per period: payroll and salary payment documents, personal income tax finalisation, and social insurance contribution records. Build a gap-explanation table separating the documented legitimate part, the non-covered part, and the substantive gap, with a handling plan, rather than letting the whole gap be presumed evasion.
How are late amounts calculated on a back-assessed gap?
Late amounts run at 0.03% per day on the back-assessed sum for the number of late days under Article 40 of the Social Insurance Law 41/2024/QH15, accumulated over the entire under-contribution period. For gaps running for years across a wide workforce, the late amount alone can equal a significant proportion of the principal, before administrative fines.
Practical recommendations
In an era when tax and insurance data are interconnected, a wage gap between the two systems is no longer a safe grey zone but a debt awaiting matching day. Employers should run this reconciliation themselves once a year as part of internal audit, and resolve substantive gaps by bringing the contribution base back to the rules before an inspection team does it for them, with fines attached.
This article has been quality-reviewed by the FLAW AI Legal Council