Correctly Sum Two Or More Columns in Power Query and Power BI

Let’s say you have a few numerical columns [A], [B] and [C] in your table and want to sum them to the new column in Power Query or Query Editor in Power BI.

Three numerical columns we want to sum in the new column

In Power Query we have special buttons for this:

Sum of columns in Power Query is easy as 1-2-3

For example, we want to sum columns [A] and [C]. Just click (holding Ctrl button) column headers you want to sum, then go to “Add Column” – “Standard” – “Add”, and you’ll get a new column named “Addition” with the row-by-row sum of desired columns:

Sum of columns [A] and [C] – sure it is

If we want to add three columns at a time, then we’ll also get a desired result:

What we’ve expected? Just simple sum of [A]+[B]+[C]

But if in this table we want so sum columns [A] and [B], we are not expecting a pitfall, aren’t we?

What could go wrong?

The reason of this behaviour is simple and it reveals itself when we look at our data a little bit close: there is a null in column [B] in that row. In Power Query formula language (M) the expression null + value always returns a null (see this excellent post of Ben Gribaudo about null type and operations with null values).

But why we get a correct result when we sum up three columns? It is because Power Query uses different formulas when we sum two columns or three and more columns:

List.Sum function used in this case ignores null values and sums up only numerical values. Indeed, it gives more intuitive result, but on the contrary has not such intuitive syntax of simple addition.

I do not know what is the reason of such difference, and already complained to the development team. But if you rely on the buttons there, then you have to be aware of such behaviour.

What is the possible solutions there? It depends on what you want to get as a result, but in any case you should take a look at the formula bar and decide what to correct there:

  • If the logic of your calculations assume that value + null = null, then you should use simple + symbol between column names.
  • If you want to get value + null = value, then you should use List.Sum finction, like in that example: List.Sum({[A], [B], [C]})

THE SAME BEHAVIOR Power Query shows when you’ll try to multiply two columns and three or more columns: with two columns there will be the simple * symbol, with three or more columns there will be List.Product function used.

Ok, it is a really short post which I planned to (and ought to) write a long time ago…

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  1. Hey! I am doing a course in Power BI where I am supposed to divide one column by the other, which seems quite easy when they show it in the video. However, when I choose both columns, the “standard” tab becomes grey and is no longer possible to use. This is however not the case if I only mark one column. Is there a simple explanation to this that you know of? 🙂

  2. What about to sum all the values in a particular column? For example, summing up all the values in column A?

    • Maxim Zelensky
      March 15, 2021 - 14:08

      I already answered this question but can repeat: List.Sum(stepname[ColumnA]) to rescue 🙂

  3. But can you show total of column A in a new column with list.sum function?

    • Maxim Zelensky
      May 6, 2019 - 11:12

      Yes, if you NEED it, you can. Formula for a new column should be like this:
      = List.Sum(PreviousStepName[Column A])
      it will return the same number (sum of ColumnA) for each row in the new column.


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