Pillar Two: Is the Real Challenge the 15% Minimum Tax or Data Quality?

As Pillar Two rules continue to take effect across an increasing number of jurisdictions, multinational enterprise (MNE) groups are experiencing the first year of implementation of the Global Minimum Tax regime.

While initial discussions largely focused on the 15% global minimum tax, early implementation experience suggests that the most significant challenge often lies elsewhere.

For many groups, the greatest obstacle is not calculating the additional tax liability itself, but obtaining accurate, consistent and reliable data capable of supporting those calculations.

This message is increasingly reflected in the OECD's GloBE Model Rules, Consolidated Commentary, Administrative Guidance, and more recent implementation tools. Across these publications, the OECD consistently emphasizes that successful Pillar Two compliance depends not only on the correct interpretation of the rules, but also on robust data governance, reliable financial information and effective internal processes.

Why Is Pillar Two Different from Traditional Corporate Tax Rules?

Pillar Two goes far beyond a conventional corporate income tax calculation.

For each jurisdiction, companies are required to analyse and reconcile, among others:

• Financial accounting data
• Current and deferred tax positions
• Intra-group transactions
• Tax incentives and tax credits
• Corporate restructurings
• Permanent and temporary differences

All of these elements must ultimately be assessed under a single GloBE methodology.

Consequently, producing an accurate Pillar Two calculation is no longer solely a technical tax exercise. It also depends on the quality, consistency and reliability of data collected from multiple financial and operational systems.

What Does the Social Content Creator Exemption Cover?

Experience from the first Pillar Two implementation projects indicates that companies often spend considerably more time on data preparation than on the tax calculation itself.

In practice, the most time-consuming aspects typically include:

• Collecting data from multiple systems
• Standardising information across jurisdictions
• Completing missing data points, and
• Documenting assumptions and calculation methodologies

Recent OECD implementation materials further reinforce this approach. Guidance relating to the GloBE Information Return (GIR), Safe Harbour mechanisms, and the Qualified Domestic Minimum Top-up Tax (QDMTT) continues to place increasing emphasis on standardised data sets, documentation and audit-ready information throughout the compliance process.

Does Safe Harbour Eliminate the Data Challenge?

The Transitional Safe Harbour rules undoubtedly provide significant compliance relief for many multinational groups.

However, applying a Safe Harbour does not:

• Reduce the importance of data quality
• Eliminate the need to validate underlying calculations, or
• Remove documentation requirements for future tax audits

In other words, Safe Harbour may simplify the tax computation—but it does not eliminate the need for robust data governance.

What Does This Mean for Türkiye?

With Türkiye implementing the Pillar Two framework, in-scope groups are required to adapt not only to a new international tax regime, but also to entirely new reporting, governance and data management requirements.

As a result, Pillar Two is no longer a project that can be managed solely by the tax department.

Successful implementation requires close coordination between tax, finance, accounting, consolidation and information technology teams, making Pillar Two a cross-functional transformation project rather than a purely tax compliance exercise.

Conclusion

The first year of Pillar Two implementation has delivered a clear message:

Success depends not only on calculating the correct amount of tax, but on building the data infrastructure capable of supporting that calculation.

Reliable tax outcomes are only possible where reliable data exists.

Accordingly, companies may wish to ask themselves a more fundamental question:

Do we merely have the technical expertise to perform a Pillar Two calculation, or do we genuinely have the data infrastructure required to support it?

As tax authorities begin to review Pillar Two filings, it is reasonable to expect that scrutiny will extend beyond the amount of top-up tax calculated. Increasing attention is also likely to be given to the quality of underlying data, the supporting documentation and the robustness of internal control frameworks.