The Platform for Collaboration on Tax (PCT)—a joint initiative of the International Monetary Fund (IMF), the Organisation for Economic Co-operation and Development (OECD), the United Nations (UN), and the World Bank Group (WBG)—held a virtual roundtable on the Impact of Development Co-operation on Tax on May 5, 2026. The event brought together over 40 participants from international and regional organizations, development partners, think tanks, technical assistance providers, and countries to discuss how to improve the monitoring and evaluation of tax reforms and the impact of international support on taxation.

Context

The importance of improving tax revenues in developing countries has never been clearer.

Other sources of financing for development face significant challenges, while taxation remains the largest source of financing for most countries and offers clear potential for improvement.

There has been significant progress in supporting the development of tax systems in developing countries in recent years, with the range and modalities of support expanding alongside improvements in data and diagnostics. The PCT report to the G20 in 2025, Progress in Strengthening Frameworks for Building Tax Capacity, summarized this progress while also highlighting remaining challenges, particularly in tracking the impact of both country-led tax reform and international support. Tighter external resourcing makes it more important than ever to improve the effectiveness of support on tax. Many speakers at the recent PCT Tax and Development Conference in Tokyo (March 2–3, 2026) emphasized this same point.

Participants reiterated the challenges faced by stakeholders working on tax and development in measuring impact effectively and using those insights to support country-led priorities while meeting provider needs. A recurring theme throughout the discussion was the importance of understanding whose goals are being measured and from whose perspective. Countries have their own priorities and definitions of success, and international support should be assessed accordingly.

The roundtable discussion was organized into two sessions. The first focused on clarifying the range of impacts sought in tax and development, while the second explored the existing and potential tools and data available to track these impacts.

Identifying the ideal – What are the impacts that we want to see in tax and development?

Tax-to-GDP – the (flawed) starting point

Increased tax revenue is often the primary impact being sought, but participants noted that measuring progress through tax-to-GDP ratios can be challenging. These ratios are influenced by many external economic factors and therefore provide only a partial picture. While there was broad agreement that tax-to-GDP ratios remain important—particularly given evidence of the significance of exceeding the 15 percent threshold for sustainable development—participants emphasized the need to prioritize a broader set of metrics and identify revenue precursors that can better capture progress.

Impacts beyond revenues – behaviours and distribution

Participants highlighted that many reforms seek impacts beyond revenue generation. Fiscal measures designed to encourage behavioural changes, such as supporting the energy transition, may not be adequately captured through revenue indicators alone.

The importance of understanding the distributional impacts of taxation was also emphasized. Participants noted that these impacts influence the social contract and public trust in tax systems. Improving transparency, fairness, and confidence in tax administration was therefore seen as a key component of sustainable tax systems.

Tax administration reforms – more challenging to track?

The discussion also examined the challenges of tracking the impact of tax administration reforms. The pathways through which administrative improvements translate into revenue gains are often indirect and difficult to measure. Developing meaningful indicators that reflect simpler, clearer, and more transparent tax systems remains an important challenge.

Tracking impact in context – the “missing middle”, universal frameworks, and country priorities

Participants discussed the different levels at which impact can be measured and noted the existence of a “missing middle,” where interactions between programs and initiatives are often difficult to capture. While some participants suggested developing a more universal framework for evaluating development cooperation on tax, there was also strong recognition of the need to tailor approaches to country-specific contexts and priorities.

Examples from Small Island Developing States (SIDS) highlighted how country circumstances shape priorities. In these contexts, taxpayer education and efforts to strengthen relationships between taxpayers and tax administrations can be especially important. Participants agreed that countries’ own objectives should remain the starting point for assessing success.

Mapping the ideal to reality – How can we practically track impact in tax and development?

Data gaps or gaps in data?

Participants recognized the significant progress made in recent years in tax data and diagnostics but questioned whether awareness and use of these resources are keeping pace. Countries are increasingly collecting data on their tax systems, yet there is often untapped potential to analyze and benchmark that information more effectively.

Several participants argued that the challenge is not always a lack of data but rather a lack of understanding and utilization of existing information. Before introducing new reporting requirements, efforts should be made to maximize the value of currently available data and improve how it is presented and interpreted.

At the same time, genuine data gaps remain in areas such as tax expenditures, where information is still unavailable or incomplete in many countries. Even where data exists, access may be restricted due to legal, political, or institutional barriers.

Making better use of qualitative data

Participants stressed the importance of qualitative evidence in understanding reform outcomes. Case studies can provide valuable insights into both the impacts of reforms and the processes through which change occurs, including political economy considerations.

However, participants noted that many case studies focus narrowly on individual interventions rather than taking a broader view across multiple actors supporting reform efforts. There was interest in consolidating existing case studies and developing more comprehensive “transformation stories” that capture the wider reform journey.

The potential role of artificial intelligence was also discussed. Participants suggested that large language models may be particularly useful in synthesizing qualitative evidence, although their capabilities in complex quantitative analysis remain more limited.

Communicating impact

Participants emphasized that collecting evidence is only part of the challenge. Communicating results effectively is equally important. Different audiences require different approaches, and there is a need to communicate both successes and failures in ways that support learning and accountability.

The role for the PCT

Participants identified several areas where the PCT could contribute:

• Curating best practices, case studies, and transformation stories.
• Balancing quantitative and qualitative evidence for different audiences.
• Improving awareness of and access to existing data and evidence.
• Developing shared good practices for monitoring and evaluation frameworks while recognizing country-specific contexts.
• Providing a “health check” on progress in tax system development.
• Supporting evidence-based allocation of official development assistance for tax.

The PCT partners will continue discussing these and other ideas in the coming weeks as they develop a workplan in this area.

What was clear from the discussions is that this challenge cannot be addressed by the PCT alone. Participants expressed strong interest in continuing and expanding collaboration and shared learning on strengthening monitoring and evaluation in tax and development.