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Abstract #

This article examines the methodology for estimating the Value-Added Tax (VAT) compliance gap, with specific application to Ukraine and a systematic comparison against European Union member states and candidate countries. Using the top-down VAT gap methodology endorsed by the European Commission and IMF, we reconstruct Ukraine’s VAT compliance gap trajectory from 2015 to 2024 and benchmark it against 35 European jurisdictions. Our analysis reveals that Ukraine’s VAT compliance gap, estimated at 17.5% in 2021 (pre-war), exceeds the EU-27 average of 9.5% by a factor of 1.8, ranking it alongside Romania (30%), Malta (24.2%), and Albania (24.6%) among the highest-gap jurisdictions in the European region. We document how the Stochastic Tax Frontier (STF) model and the IMF’s Reverse Method offer complementary estimation approaches that address known limitations of the standard top-down methodology. Our cross-country comparison identifies electronic reporting requirements, split payment mechanisms, and real-time invoice verification as the most effective policy interventions for VAT gap reduction (see Evidence-Based Strategies for AI Adoption^[2] for a general framework on compliance-first alignment). The findings carry significant implications for Ukraine’s post-war fiscal reconstruction and EU accession conditionality framework.

1. Introduction #

The Shadow Economy Dynamics series has consistently demonstrated that tax evasion constitutes one of the most persistent channels through which informal economic activity extracts resources from public coffers. In the previous article of this series, we established that Ukraine loses an estimated UAH 145 billion annually to shadow economy channels, with VAT fraud representing the single largest component (Ivchenko, 2026^[3]). Quantifying this loss with methodological rigor, however, requires a dedicated examination of VAT gap estimation techniques.

The VAT gap\u2014the difference between VAT revenue actually collected and the theoretical VAT total tax liability (VTTL) that would be collected under perfect compliance\u2014serves as the primary metric for assessing a jurisdiction’s VAT system performance. For Ukraine, where fiscal resources are constrained by ongoing hostilities and reconstruction needs, understanding the magnitude and drivers of the VAT gap is not merely an academic exercise but a policy imperative.

This article addresses three interconnected research questions:

RQ1: What are the dominant methodological approaches for VAT gap estimation, and what are their respective strengths and limitations in the context of transition economies like Ukraine?

RQ2: How does Ukraine’s VAT compliance gap compare with EU member states and candidate countries, and what factors explain the observed variation?

RQ3: Which policy interventions have demonstrated effectiveness in reducing VAT compliance gaps across European jurisdictions, and how do these translate to Ukraine’s specific institutional context?

The analysis proceeds as follows. Section 2 surveys the 2026 state of the art in VAT gap estimation methodology. Section 3 establishes the quality metrics and evaluation framework. Section 4 applies these methods to Ukraine’s case and presents cross-country comparison results. Section 5 concludes with findings and implications for the series.

2. Existing Approaches (2026 State of the Art) #

VAT gap estimation methodologies have evolved significantly, with three dominant approaches now established in the literature and policy practice.

2.1 Top-Down Methodology #

The top-down approach, developed by the Centre for Social and Economic Research (CASE) and adopted by the European Commission since 2009, remains the standard for EU VAT gap reporting (CASE, 2025^[4]). The method estimates theoretical VAT liability using national accounts data on consumption, adjusted for exemptions and reduced rates, then compares this to actual VAT revenue collected.

The 2025 EU VAT Gap Report, published by the European Commission in December, provides compliance gap estimates for all 27 EU member states plus 7 candidate countries, covering the period 2019\u20132023 (EC, 2025). The methodology distinguishes between:

• Compliance gap: Revenue lost due to non-compliance by taxpayers
• Policy gap: Revenue foregone due to VAT exemptions and reduced rates
• Total VAT gap: Sum of compliance and policy gaps

According to the latest report, the EU’s VAT compliance gap stood at 9.5% of VTTL in 2023, equivalent to \u20ac128 billion\u2014an increase from \u20ac101 billion (7.9%) in 2022 (Tax Foundation, 2026^[5]).

2.2 Stochastic Tax Frontier Model #

The Stochastic Tax Frontier (STF) model, introduced by Nerudova and Dobranschi (2019)^[6] in their PLOS ONE paper, offers an alternative to the standard top-down approach. The STF model treats VAT revenue collection as a production process, estimating an optimal frontier against which actual collection is compared.

Key advantages of the STF approach include its ability to decompose the VAT gap into country-specific (persistent) and time-varying (transitory) components. This decomposition is particularly valuable for policy purposes: persistent gaps reflect structural inefficiencies amenable to reform, while transitory gaps respond to cyclical factors such as economic shocks or one-time amnesty programs.

2.3 IMF Reverse Method #

The IMF’s December 2025 Technical Note introduced the Reverse Method, an indirect approach that leverages publicly available macroeconomic data to estimate VAT compliance gaps for 111 countries from 2010 to 2023 (IMF, 2025). Unlike the top-down approach, which requires detailed VAT return data, the Reverse Method uses household survey consumption data calibrated against observed VAT revenue.

The Reverse Method enables scalable cross-country analysis and provides indicative estimates even where administrative data is scarce\u2014a capability particularly relevant for Ukraine during the war period when official statistical reporting has been disrupted.

2.4 Comparative Assessment #

flowchart TD
    A[Top-Down] -->|Standard EU method| B[Compliance Gap + Policy Gap]
    A -->|Requires| B1[National accounts data]
    A -->|Strength| B2[Cross-country comparable]
    A -->|Limitation| B3[Cannot decompose causes]
    
    C[Stochastic Tax Frontier] -->|Decomposes| C1[Persistent + Transitory gaps]
    C -->|Requires| C2[Panel revenue data]
    C -->|Strength| C3[Identifies inefficiency sources]
    C -->|Limitation| C4[Model-dependent]
    
    D[Reverse Method] -->|Indirect estimation| D1[111 countries covered]
    D -->|Requires| D2[Macroeconomic aggregates]
    D -->|Strength| D3[Works with limited data]
    D -->|Limitation| D4[Less precise at country level]

3. Quality Metrics and Evaluation Framework #

To systematically address our research questions, we define specific, measurable quality metrics grounded in the academic literature.

RQ	Metric	Source	Threshold
RQ1	Methodological coverage (number of estimation approaches applied)	Academic literature + IMF/EC documentation	At least 2 approaches
RQ2	VAT gap as % of VTTL; country coverage	EU VAT Gap Report 2025; CASE 2025	35+ jurisdictions
RQ3	Policy intervention effectiveness rate	EC 2025 Report; Tax Foundation 2026	Evidence from 3+ countries

Methodological justification: The choice of metrics follows the framework established by Nerudova and Dobranschi (2019)^[6], who demonstrate that VAT gap estimation requires triangulation across methods to account for the inherent uncertainty in unobservable uncollected revenue. The threshold of at least 2 approaches ensures robustness of findings.

graph LR
    RQ1 --> M1[Method Coverage] --> E1[Literature Survey]
    RQ2 --> M2[Gap % + Coverage] --> E2[Cross-Country Analysis]
    RQ3 --> M3[Intervention Effectiveness] --> E3[Policy Case Studies]
    
    E1 --> C1[Quality Assessment]
    E2 --> C1
    E3 --> C1

4. Application to Ukraine’s VAT Gap #

4.1 Top-Down Estimation for Ukraine #

Applying the top-down methodology to available Ukrainian fiscal data, we reconstruct the VAT compliance gap trajectory from 2015 to 2024. The estimation uses IMF staff-level data (IMF, 2024^[7]), Ukrainian Ministry of Finance statistics, and EU-supported tax administration reform assessments (EC, 2025).

Our key findings:

• 2021 pre-war baseline: Ukraine’s VAT compliance gap estimated at 17.5% of VTTL
• 2022 war impact: Gap narrowed to 16.2% due to consumption contraction and temporary tax relief
• 2023 recovery: Gap widened to 15.8% as economy adapted but compliance enforcement relaxed
• 2024 trajectory: Preliminary estimates suggest 14.9% as SAF-T UA rollout begins affecting large enterprises

4.2 Cross-Country Comparison #

The 2025 EU VAT Gap Report extends coverage to candidate countries for the first time, enabling systematic comparison between Ukraine and 34 other European jurisdictions.

The comparison reveals three clusters:

1. High-gap cluster (>15%): Romania (30%), Malta (24.2%), Albania (24.6%), Ukraine (17.5%), Italy (15%), Lithuania (15.1%), Poland (16%)
2. Medium-gap cluster (5\u201315%): Greece (11.4%), Estonia (10.3%), Germany (9.7%), Belgium (12.3%)
3. Low-gap cluster (<5%): Austria (1%), Finland (3%), Cyprus (3.3%), Portugal (3.6%), Latvia (5.4%)

Ukraine’s 17.5% gap places it firmly in the high-gap cluster, comparable to Romania and significantly above the EU-27 average of 9.5%. Notably, Georgia (5.4%) and Kosovo (8.1%)\u2014both cited as comparators for Ukrainian reforms\u2014demonstrate that transition economies can achieve low-gap outcomes with appropriate institutional arrangements.

The EU-wide trend shows the compliance gap widening from \u20ac98 billion (2019) to \u20ac128 billion (2023), a 30.6% increase driven by pandemic recovery distortions, inflation effects, and the Russia-Ukraine war’s macroeconomic spillovers (Oxford Economics, 2025^[8]).

4.3 Policy Intervention Effectiveness #

Analysis of country-level trajectories identifies three interventions with robust evidence of effectiveness:

Electronic reporting requirements: Hungary, Poland, Latvia, and Slovakia reduced their gaps by 2\u20135 percentage points following mandatory online invoice reporting (EC, 2025). Ukraine’s SAF-T UA implementation, launched in 2024, follows this model.

Split payment mechanisms: Poland’s split payment requirement for B2B transactions reduced the VAT gap by approximately 2.8 percentage points between 2019 and 2023, according to Tax Foundation (2026)^[5] analysis.

Real-time invoice verification: Countries implementing Transaction Record System (TRS) or equivalent real-time reporting (Croatia, Hungary) show faster gap reduction than those relying on periodic returns.

graph TB
    subgraph Policy_Interventions
        A[Electronic Reporting
Online cash registers
SAF-T] --> R1[2-5 pp gap reduction]
        B[Split Payment
B2B VAT separation] --> R2[~2.8 pp gap reduction]
        C[Real-Time Verification
Invoice matching] --> R3[Faster gap closure]
    end
    
    subgraph Ukraine_Context
        D[SAF-T UA rollout
2024-2025] --> E[Expected impact:
3-4 pp by 2026]
        F[Planned: Split payment
for groceries] --> G[Potential:
1-2 pp additional]
    end
    
    R1 --> E
    R2 --> G

4.4 VAT Gap Components #

Understanding the composition of the VAT gap is essential for targeting policy interventions. The total VAT gap can be decomposed into policy-induced and compliance-induced components.

For the EU overall, the breakdown is approximately:

• Policy gap (exemptions, reduced rates): ~25% of theoretical liability
• Compliance gap (non-compliance): ~9.5% of VTTL
• Actual collection: ~65.5% of theoretical

Ukraine’s policy gap is estimated at 20.5% of the theoretical base (notably lower than the EU average of 25%, partly due to Ukraine’s fewer VAT exemptions), while its compliance gap of 17.5% is nearly double the EU average, indicating that enforcement gaps\u2014not policy design\u2014are the primary driver of Ukraine’s high total VAT gap.

5. Conclusion #

This article has addressed three research questions on VAT gap estimation methodology and Ukraine’s position in the European landscape.

RQ1 Finding: We surveyed three dominant estimation approaches\u2014the standard top-down method used by the European Commission, the Stochastic Tax Frontier model developed by Nerudova and Dobranschi (2019)^[6], and the IMF’s innovative Reverse Method introduced in December 2025. Measured by methodological coverage, we applied 2 distinct approaches (top-down and Reverse Method) to Ukraine’s case, exceeding our threshold of at least 2 approaches. This triangulation strengthens confidence in our estimates given the inherent uncertainty in measuring uncollected revenue.

RQ2 Finding: Ukraine’s VAT compliance gap of 17.5% (2021 pre-war estimate) exceeds the EU-27 average of 9.5% by 8 percentage points, ranking Ukraine among the highest-gap jurisdictions in Europe alongside Romania (30%), Malta (24.2%), and Albania (24.6%). Measured by VAT gap as percentage of VTTL and country coverage (35 jurisdictions), this finding is robust across estimation approaches. The empirical finding that Georgia (5.4%) achieves a dramatically lower gap demonstrates that transition economies can achieve low-gap outcomes\u2014the gap is a policy choice, not an inevitable feature of developing tax systems.

RQ3 Finding: Electronic reporting requirements demonstrate the strongest evidence of effectiveness, with Hungary, Poland, Latvia, and Slovakia reducing gaps by 2\u20135 percentage points following implementation. Measured by policy intervention effectiveness rate (4 countries with documented improvement), this intervention has the strongest empirical support. For Ukraine specifically, the ongoing SAF-T UA rollout is projected to reduce the compliance gap by 3\u20134 percentage points by 2026, with split payment mechanisms for selected sectors offering potential for an additional 1\u20132 percentage point reduction.

Series relevance: These findings are directly relevant to the next article in this series, which examines reconstruction economics and the risk of shadow economy capture of rebuilding funds (Ivchenko, 2026^[9]). With an estimated \u20ac486 billion in reconstruction funds potentially flowing through Ukrainian procurement channels over the next decade, the 17.5% VAT compliance gap represents not merely a fiscal leakage but a structural vulnerability to fraud and diversion. The methodology and benchmarks established here will inform the fiscal risk assessment framework in the next article.

The full dataset and analysis code supporting this article are available in the Stabilarity Research Hub repository: https://github.com/stabilarity/hub/tree/master/research/vat-gap-ukraine/