Understanding Power BI Totals: The Math, the Model, and the Misconceptions

The long-running debate around how Power BI calculates totals in tables and matrices has been part of the community conversation for years. Greg Deckler has kept the topic alive through his ongoing “broken totals” posts on social media, often suggesting that Power BI should include a simple toggle to make totals behave more like Excel. His continued campaign prompted a detailed reply from Daniel Otykier in his article No More Measure Totals Shenanigans, and earlier, Diego Scalioni explored how DAX evaluates totals internally in his post Cache me if you can: DAX Totals behind the scenes.

This blog brings all those perspectives together from a scientific and comparative angle. It looks at how totals are calculated in Power BI and compares that behaviour with Tableau, Excel, Paginated Reports, QlikView and even T-SQL. The goal is not to take sides, but to clear up the confusion around what is happening under the hood.

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Power BI’s Broken Totals – Myth Debunked

Are Power BI Totals Really Broken?

Let’s get one thing clear right at the start, no, Power BI totals are not broken. There is no “it depends” this time. What some interpret as broken behaviour is actually how DAX and the underlying model are designed to work.

This post is not personal, it is purely scientific and technical. While I have great respect for Greg and his significant contributions to the Power BI community, I disagree with the use of the word “BROKEN.” It sounds dramatic but does not reflect the full truth. Totals in Power BI behave exactly as the model and the maths define them to. Want to know why? Keep reading.

Why this matters

When someone with Greg’s influence keeps saying totals are “broken”, it really affects how new users see Power BI. Some even start thinking the tool itself is not reliable, when what they are seeing is actually how different reporting tools do their calculations in different ways.

It helps to know the main calculation styles that these tools use:

  • Cell based: This is what you get in worksheet formulas and classic PivotTables that use Excel ranges. Totals are just simple sums of the shown items, with no model or relationships behind the scene.
  • Model driven: This is how Power BI works and also Excel PivotTables that use the Data Model (Power Pivot) or connect to a tabular dataset. Measures are calculated again for every context, so totals depend on how filters and relationships are set.
  • Query driven: Tools like Paginated Reports work this way. The report runs a query, for example SQL or DAX, gets the dataset, and then sums or averages values in the report design. The author decides how each total should be calculated.
  • Hybrid (query and context driven): Tableau fits in here. It gets the data through a query but also lets you change the level of detail and how totals behave in the visual. So sometimes it acts like a query tool and sometimes more like a model one.

Most of the confusion happens when people compare results from these tools as if they all worked the same way. Once you understand the difference between cell based, model driven, query driven, and hybrid tools, the way Power BI shows its totals starts to make full sense.

The problem that started it

Greg’s long-running example uses a small table with a single column of numbers and a DAX measure like this:

SUMX(SampleData, SampleData[Amount]) - 10

In the total row, the result shows 590, while he expects 580 (two groups of 290 each). Based on that, he argues that Power BI totals are “wrong”.

But DAX is only doing what it is told to do. In this measure, the subtraction of 10 happens after the total amount is calculated, not for each row. If the intention was to take 10 away per row, then the measure should be written like this:

SUMX(SampleData, SampleData[Amount] - 10)

This version gives the expected 580 because the subtraction now happens at the lowest level of detail, which is per row.

This might look like a small detail, but it is exactly where most of the confusion around totals begins. The difference is not about Power BI being wrong; it is about understanding where in the calculation the operation happens.

The math behind it

Before we look at the numbers, let’s first talk about what we are trying to do. We Greg’s small and very simple table that shows some amounts by Category and Colour:

CategoryColourAmount
ARed100
AGreen100
ABlue100
BRed100
BGreen100
BBlue100
Continue reading “Understanding Power BI Totals: The Math, the Model, and the Misconceptions”

Power BI Desktop Versions Demystified: Part 1, Power BI Desktop and Power BI Desktop RS

If you are a Power BI power user, you may have wondered: how many versions of Power BI Desktop are there? The quick answer is: it depends!

Depending on your organisation’s preferences, data governance requirements, and the platforms you intend to use for report deployment you may use either Power BI Desktop, the “standard version”, or Power BI Desktop RS (Report Server). Power BI Desktop has variations tailored to meet specific needs, such as cloud-based analytics or on-premises reporting. While many users might only encounter the standard version, there’s another important variant for specialised scenarios.

Power BI Desktop comes in two primary versions:

  1. Power BI Desktop:
    This is the standard version most users rely on. It’s the go-to tool for transforming data, creating semantic models, and building interactive reports. This version is designed to seamlessly integrate with the Power BI Service hosted on Microsoft Fabric, enabling cloud-based sharing, collaboration, and advanced features like Direct LakeAI-driven insights, and more. Regular updates ensure that this version includes the latest features and innovations, such as new Power Query and DAX functions, enhanced visuals, and cutting-edge integrations.
  1. Power BI Desktop RS (Report Server):
    This is a specialised version of Power BI Desktop designed to work exclusively with Power BI Report Server, a locally hosted reporting platform. It is tailored for organisations that prefer to keep their data and reports on-premises due to regulatory, security, or strategic reasons, avoiding reliance on cloud services like the Power BI Service on Microsoft Fabric. Although the two versions look nearly identical in functionality, they serve distinct purposes. Power BI Desktop RS is specifically aligned with the capabilities of Power BI Report Server, supporting features available up to the latest release cycle of the server. For instance, Power BI Desktop RS updates are less frequent; typically released every few months, in line with Power BI Report Server’s update schedule; making it slightly behind the standard version in terms of cutting-edge features. However, it ensures stability and compatibility for on-premises deployments.
Continue reading “Power BI Desktop Versions Demystified: Part 1, Power BI Desktop and Power BI Desktop RS”

Optimising OData Refresh Performance in Power Query for Power BI and Excel

OData has been adopted by many software solutions and has been around for many years. Most solutions are using the OData is to serve their transactional processes. But as we know, Power BI is an analytical solution that can fetch hundreds of thousands (or millions) rows of data in a single table. So, obviously, OData is not optimised for that kind of purpose. One of the biggest challenges many Power BI developers face when working with OData connections is performance issues. The performance depends on numerous factors such as the size of tables in the backend database that the OData connection is serving, peak read data volume over periods of time, throttling mechanism to control over-utilisation of resources etc…

So, generally speaking, we do not expect to get a blazing fast data refresh performance over OData connections, that’s why in many cases using OData connections for analytical tools such as Power BI is discouraged. So, what are the solutions or alternatives if we do not use OData connections in Power BI? Well, the best solution is to migrate the data into an intermediary repository, such as Azure SQL Database or Azure Data Lake Store or even a simple Azure Storage Account, then connect from Power BI to that database. We must decide on the intermediary repository depending on the business requirements, technology preferences, costs, desired data latency, future support requirement and expertise etc…

But, what if we do not have any other options for now, and we have to use OData connection in Power BI without blasting the size and costs of the project by moving the data to an intermediary space? And.. let’s face it, many organisations dislike the idea of using an intermediary space for various reasons. The simplest one is that they simply cannot afford the associated costs of using intermediary storage or they do not have the expertise to support the solution in long term.

In this post, I am not discussing the solutions involving any alternatives; instead, I provide some tips and tricks that can improve the performance of your data refreshes over OData connections in Power BI.

Notes

The tips in this post will not give you blazing-fast data refresh performance over OData, but they will help you to improve the data refresh performance. So if you take all the actions explained in this post and you still do not get an acceptable performance, then you might need to think about the alternatives and move your data into a central repository.

If you are getting data from a D365 data source, you may want to look at some alternatives to OData connection such as Dataverse (SQL Endpoint), D365 Dataverse (Legacy) or Common Data Services (CDS). But keep in mind, even those connectors have some limitations and might not give you an acceptable data refresh performance. For instance, Dataverse (SQL Endpoint) has 80MB table size limitation. There might be some other reasons for not getting a good performance over those connections such as having extra wide tables. Believe me, I’ve seen some tables with more than 800 columns.

Some suggestions in this post apply to other data sources and are not limited to OData connections only.

Suggestion 1: Measure the data source size

It is always good to have an idea of the size of the data source we are dealing with and OData connection is no different. In fact, the backend tables on OData sources can be wast. I wrote a blog post around that before, so I suggest you use the custom function I wrote to understand the size of the data source. If your data source is large, then the query in that post takes a long time to get the results, but you can filter the tables to get the results quicker.

Suggestion 2: Avoid getting throttled

As mentioned earlier, many solutions have some throttling mechanisms to control the over-utilisation of resources. Sending many API requests may trigger throttling which limits our access to the data for a short period of time. During that period, our calls are redirected to a different URL.

Tip 1: Disabling Parallel Loading of Tables

One of the many reasons that Power BI requests many API calls is loading the data into multiple tables in Parallel. We can disable this setting from Power BI Desktop by following these steps:

  1. Click the File menu
  2. Click Options and settings
  3. Click Options
  4. Click the Data Load tab from the CURREN FILE section
  5. Untick the Enable parallel loading of tables option
Disabling Parallel Loading of Tables in Power BI
Disabling Parallel Loading of Tables in Power BI Desktop
Continue reading “Optimising OData Refresh Performance in Power Query for Power BI and Excel”