Tableau Tip Tuesday: How to Compare Current YTD to Prior YTD

This week's tip came from a question from Andrzej Szczurko on week one's tip from Lorna:

How would you do year to date percent difference when you only have data for first 3 months in the current year? For example when you have data for the current year from January to March for 2018 and you want to compare it to January to March from 2017 and calculate percent difference then?

This is a very common business question. In this video I show you how to use level of detail expressions to calculate these two fields plus the difference.

NOTE: In the video, I have the Year over Year calculation backwards. The formula should be: SUM([CY Sales])-SUM([PY Sales])