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.