title: Compare totals for the same partial date range year-over-year in DAX / Power BI
body: <p>I'm trying to create a table which shows a sum of monthly values for one year compared to the last year's totals (structured as the screenshot below):
  <a href="https://i.stack.imgur.com/PkZDw.png" rel="nofollow noreferrer">Monthly Comparison</a></p>
  
  <p>However, the caveat I'm dealing with is comparing the most current month, which will always contain partial month data (unless it's the last day of the month), to the same date range of the previous year.  In the screenshot I attached, our data for January 2018 only goes through January 22nd.  However, it's comparing it to the <em>full</em> month of January from 2017, whereas we want that total to be January 1st - 22nd, 2017: <a href="https://i.stack.imgur.com/LUbTB.png" rel="nofollow noreferrer">Value That Needs to be Updated</a>.</p>
  
  <p>I've tried messing around with various MTD and cumulative totals, but I can't seem to get the logic to work while keeping the aggregation to the monthly level.  Any idea what type of logic needs to used in order to compare year-over-year totals, but only do a partial sum for the same date range of a month that is currently in progress?</p>
  
  <p>Thanks in advance.</p>