DAX Date Calculations Not Working in Power BI Desktop? Here’s a fix.

Power BI offers a number of different ways to access data needed for data visualization and analysis. The reasons for selecting Power BI Desktop or Excel Power Pivot are more than likely going to change after I write this, but right now, Excel provides the ability to upgrade to a Tabular SSAS model, where Power BI Desktop does not. While Power BI Desktop and Excel both provide the ability to create formulas in DAX, only in Excel Power Pivot do you have the ability to use DAX Time and Date based calculations, but you can make Power BI Desktop do it, with help from Excel.

DAX Time and Date Calculations won’t work in Power BI Desktop

The DAX language has a number of Time and Date Calculations which contained common functions which relate to a given time frame. Here’s a list of Time and Date DAX Functions from Microsoft. These are very useful functions which you may find yourself wanting to do from time to time. None of them work in Power BI Desktop. Why? Power Pivot requires you to click on the Mark as Date Table to identify a table which contains column containing a list of unique Date and Time fields for DAX Date and Time functions to work. If you don’t have a table containing a list of dates and times in your model, you cannot use any DAX Time and Date Calculations. If you need a table like this, check out my blog post on Date table generation using a CTE to create one for you.  There is no place in Power BI Desktop, as of right now, to perform the equivalent of Mark as Date table which means that DAX Time and Date Calculations like SamePriorPeriodLastYear will not work.

Example of Power BI Desktop DAX Calculation Not Working

Here’s an example of something I tried to do in Power BI Desktop. In this first screen, I have created a new measure, which I called Prior Sales, which is designed to return the PriorPeriodnotWorkingprior period, which can be something smaller than year, of the Total Sales. The DAX for Total Sales is Total Sales = sum([Sales Amount]). Note there are no errors in the Prior Sales DAX measure.


Here’s what the report using the two measures, Total Sales and Prior Sales. Prior Sales shows no values but a total. This is exactly the same thing which happens in Excel when the Mark As Date Table has not been selected.

Fixing DAX Time Date Calculations in Power BI Desktop

What can you do to fix this problem? Fortunately the fix is pretty easy, but the only trick is you have to start by creating your date table. You cannot do it later, you will have to start over. Here are the steps. In Excel, create a Power Pivot Model and add in a ImportIntoExcelDate table. You do not have to have anything else in your model. Make sure that the date table is marked as a Date Table. Save the Excel Document and exit out of it. You are going to import this file into a Power BI Desktop Model. You do this by clicking on the menu button at the top Left of Power BI Desktop and selecting the menu option Import. If you do not see this option, you probably are not using the August 20, 2015 version of Power BI Desktop. Go get the latest version of Power BI from Microsoft which you can do here. Select Excel Workbook Contents, and you will get the Import window shown below. If you read the text, which to be honest I didn’t until after I hit Start PriorPeriodWorkingand ended up in a new Power BI file, you will see that the text clearly states a “A new Power BI file will be made for you”. This means when you import data into a Power BI Desktop file, you have to do it first, you can’t excel data to an  existing file. If you import the Excel file you just created with a date table marked as date table, and then add all of the other data you are interested in using, the DAX Date Time Functions will work.

Where should I model my Data, Excel Power Pivot or Power BI Desktop?

When I last wrote about where you should model your data, there was no work around to the DAX Time Date Calculation issue. That has changed with the August 20th release. If this is the only reason that you are choosing to model in Excel, I would think again. But if you want to migrate your model to a tabular analysis services solution at some point, you will need to model in Excel to be able to use the Visual Studio project which makes that process easy. I hope you found this helpful in deciding whether you should use Excel or Power Pivot. As Microsoft continues to release fixes, the reasons for choosing one tool or another change, and when they do, check back here as I am likely to blog about it.

Yours Always

Ginger Grant

Data aficionado et SQL Raconteur

***UPDATE: Power BI has been updated to include the ability to mark a table as date table, which means that you can now join on integer based date keys. For more information see this post.


Why Power BI Desktop and Not Excel Power Pivot?

As regular readers of my blog know, I spend a time working with Power BI. Since it was released Friday, July 24, 2015, it started me thinking about all of the people who have been spending time on the previous version which, I affectionately thought of as the 4 Powers in Excel plus web. Well since the Office 365 web version is going away on December 31, 2015, I thought of the many ways you could use the new Power BI with the Excel.

Power BI on the Web is a Full Featured Application

One thing to keep in mind is that the web component of Power BI is very powerful. If you are not interested in mashing data so much as reporting on data from one source, be that SQL Server or Sales Force, select the needed data into the Dataset section of Power BI, and start working on creating visualization reports and pinning sections of those reports to a dashboard. Please note, if you create a visualization on the web there is not currently a way to download it to the desktop, meaning reports created on the web, stay on the web and you cannot download them. There is no reason to use Power BI Desktop at all. That being said, the web version is a tool not the tool, so there are times when you may need to work with either Power BI Desktop or Excel and load those models into Power BI on the web.

When do I want to use Excel for my Data Modeling and Not Power BI?

If you have created a working data mashup in Excel Power Pivot, it makes sense to load that to the web directly and use it as is. It is not possible to bring in an Excel Power Pivot model into Power Pivot Desktop, because it doesn’t read the data in Power Pivot as a data source. If you have spreadsheets containing data it will read those in, but if you have a Power Pivot model which doesn’t use any linked tables, it won’t find the data. However, if the same excel spreadsheet is loaded to the Web Version of Power BI, the data model created will be found. If you have a model created, select Add Data in the Web version to add the model and use it to generate visualizations. Power View does not have all of the modeling types which Power BI now has, so if Tree Maps or Funnel charts should be displayed either web or the desktop version of Power BI will do it. If you need to update your model in Excel, make sure that you store the model within One Drive so that the Power Pivot updates you create will be automatically migrated to the web.

When to use Power BI Desktop?

If you have anything but Excel 2013, use Power BI Desktop. Power BI Desktop provides visualizations PowerBIDesktopvery similar to Power View, which are not available outside of Excel 2013. If you would like to create a new data mashup, start by using Power BI Desktop, because it has some new modeling features which you might want to take advantage of such as Many-to-Many and Cross Filter Direction. It handles role playing dimensions the exact same way that Excel Power Pivot does, meaning you can only have one active relationship at a time. The features you need for data modeling are all their, just moved around a bit, such as using DAX to create columns or measures. Power BI Desktops allows you to create data mashups from multiple data sources as well, allowing data to be modeled from as many sources as the model will tie together.

Favorite Power BI Features

After using the previous version of Power BI, I figured I would list the features I most like in the new version, which are other reasons I would give for switching to it from Excel.

  • Colors – Getting to pick whatever color I want for my charts is wonderful. I was so getting tired of blue.
  • Data Refresh – Getting the automatic Data Refresh to work in Office 365 was complicated. The new application for refreshing Personal Gateway is wonderful as it is so easy to use. The only thing I don’t like about it is the name as I don’t see why creating a connection to a server be Personal?
  • New Visualizations – Options are great and I love having more to select from.
  • Lack of dependency on Excel Versions – It can take a while, especially in large companies to get everyone upgraded to the latest version of Excel. Now that process doesn’t keep good visualizations from happening.
  • Price – At $9.99 a month or free if you don’t mind manually refreshing your data and don’t have much data, the cost decrease helps win the argument to move to it.
  • Separation from SharePoint – the underlying administration on the web version with SharePoint in Office 365 added a layer of complexity which thankfully has been removed.

I have a lot of other thoughts on Power BI, but this is getting pretty long, so I will save my thoughts for another posting. Since it doesn’t cost anything to get started, I highly encourage everyone to start playing around with Power BI and let me know what you think.


Yours Always

Ginger Grant

Data aficionado et SQL Raconteur