I want to create a simple percent change formula in power BI. Specifically, I want to evaluate month over month %change in cost. I know that percent change can be defined in different ways, so to be clear this is the formula that I am referring to:
%change = ([current value] - [previous value])/[previous value].
Here is an example in Excel of what I want to achieve:
I cannot find a way to target a specific row in a DAX formula. It seems that power BI only wants to include aggregate values such as sum, max, etc.
As a final note, I know that PowerBI includes a percent change "quick measure". However, the 'Base Value' always requires you to select aggregate measure instead of a single row value.
As Alexis mentioned, there is no concept of referring to a specific row in DAX. It can be a hard notion for people who are used to Excel, but if you want to take advantage of PowerBi, you will have to "unlearn" Excel way of thinking.
To accomplish your goal, you need to do some data modeling first. As a common practice, replace your "Date" column with a proper Calendar table:
As a result, you will have a data model in PowerBi that looks something like this:
Once you have such structure in place, DAX is simple:
Current Month Cost = SUM(Expenses[Cost])
Previous Month Cost = CALCULATE( [Current Month Cost], PREVIOUSMONTH(Calendar[Date]))
% Change = DIVIDE( [Current Month Cost] - [Previous Month Cost], [Previous Month Cost])
来源：https://stackoverflow.com/questions/51791874/power-bi-percent-change-formula