Using DAX To Calculate Dates Between Transactions

Matt Allington needs a haircut:

I got my haircut today (pretty spiffy one too, even if I do say so myself).  While I was chatting I asked my hair dresser “on average, how often should I get my hair cut”?  She told me (for men) around 4-6 weeks.  Then I got thinking (as I do), I wonder if I could data-mine my credit card data using Power BI and find out how often I actually get my own hair cut.  It turns out I was able to do this, and this article explains the hardest part of that task – find the number of days between two transaction dates using DAX.

I’d probably end up doing this in SQL with the LAG function, but it’s good to know several ways to solve date difference problems.

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