Power BI: UDFs for Centralized DAX Logic

Key insights

• This video explains how DAX User Defined Functions (UDFs) let you centralize business logic in Power BI and reuse DAX formulas across a model.
  The feature arrived as a preview and changes how authors build and maintain complex calculations.
• To try UDFs you must enable the preview in Power BI Desktop via Options > Preview features and restart the app.
  Once active, functions appear and behave like built-in DAX objects.
• The new syntax uses the FUNCTION keyword and accepts parameters with optional types, so you can define parameterized, reusable logic.
  After you define a function, you call it in measures or calculated columns just like any standard DAX function.
• Key benefits covered include Reusability, Centralization, Maintainability, Type safety, and Modularity for clearer, safer models.
  Centralized functions reduce duplicated formulas and make updates faster and less error-prone.
• UDFs integrate into Power BI tooling as first-class items in Model Explorer and can be authored and tested in the DAX Query View and TMDL environments.
  They can accept scalars, tables, or references and can call other UDFs to build layered logic.
• Practical notes: UDFs are still a preview so expect occasional bugs and evolving behavior.
  The video shows examples and advises testing functions thoroughly and keeping business rules centralized for easier model governance.

Overview

Fernan Espejo (Solutions Abroad) published a clear, practical YouTube video explaining UDFs in Power BI and how they can centralize business rules. The video begins with setup guidance and then moves into hands-on examples that show how to author and call functions written in DAX. Along the way, Espejo highlights both small pitfalls and the broader implications for model design.

Importantly, the video situates this feature in the context of Microsoft’s preview release of DAX User Defined Functions in September 2025. Consequently, viewers should expect the capabilities to evolve and to see changes before general availability. As a result, the video presents practical tips while reminding users that the feature remains in preview.

What the video demonstrates

First, Espejo walks viewers through how to enable UDFs inside Power BI Desktop’s preview features and where to find the new objects in the model. Next, he demonstrates basic function syntax using the new FUNCTION keyword and shows simple use cases like applying a tax calculation to a sales measure. The examples make clear how a small function can replace repeated formulas across a model.

Then, he shows a second, more advanced example where functions accept parameters and can return different types, including tables. This segment emphasizes that UDFs support scalar and table inputs, enabling more dynamic calculations and richer time-intelligence scenarios. Finally, Espejo reviews managing logic across the model and highlights debugging steps when functions misbehave.

The video also uncovers a few bugs and preview limitations, and Espejo illustrates methods to work around them during development. For instance, he points out where tooling support is still catching up and where testing inside the DAX Query View and TMDL scripting environment helps. This practical troubleshooting adds value for those looking to adopt functions now rather than waiting.

Why this matters for Power BI authors

Centralizing logic with UDFs reduces formula duplication and simplifies maintenance because authors can update a rule in one place and have it apply everywhere. Moreover, optional parameter typing improves clarity and helps catch errors earlier, which makes models more robust for teams. Consequently, organizations that maintain large semantic models should find their development and peer review workflows easier.

Additionally, treating functions as first-class model objects changes collaboration patterns: functions appear in the model explorer and can be referenced by measures, columns, visuals, or other functions. This modularity encourages layering small, reusable pieces of logic to build complex behavior without repeating code. Therefore, the feature nudges DAX development closer to modern programming practices.

Tradeoffs and challenges

However, centralization introduces tradeoffs. While a single function can reduce inconsistencies, it also becomes a single point of change: a faulty update can affect many reports at once. Thus, teams must adopt version control, testing practices, and careful change management to avoid wide-ranging regressions.

Performance is another consideration. Although UDFs can simplify formulas, poorly written functions or excessive nesting may hurt query performance. In addition, preview tooling does not yet offer the same profiling and diagnostics as mature features, which means authors must invest time in performance testing and optimization. For these reasons, balancing readability, reuse, and runtime efficiency requires deliberate design choices.

Finally, adoption brings governance questions. Organizations must decide naming conventions, parameter typing standards, and ownership for shared functions. Also, compatibility with older reports and migration strategies for models without functions will take planning, especially in environments that rely on calculated columns or calculation groups today.

Practical advice and next steps

Espejo advises starting small: convert a few repetitive formulas into functions, then observe both maintainability and query behavior. Additionally, he recommends testing functions in isolation using the DAX query tools before integrating them widely, and documenting each function’s purpose and parameters to aid team adoption. Consequently, this incremental approach reduces risk and provides early evidence of benefits.

Looking ahead, teams should monitor Microsoft’s feature updates and tooling improvements as the preview progresses toward general availability. In the meantime, the video offers a balanced, hands-on guide that helps Power BI practitioners evaluate whether to adopt UDFs now or plan for a staged rollout. Ultimately, Espejo’s walkthrough equips viewers to make informed choices about centralizing business logic in their models.

Keywords

Power BI UDFs, DAX user defined functions, Reusable DAX functions, Create UDFs in Power BI, Centralize business logic in DAX, DAX function patterns, Power BI DAX best practices, Modular DAX techniques