title: Excel year-week combination calculation
body: <p>I am currently making an excel model where the date is an important aspect of it. However as the information comes from a different source it is sometimes structured in such a way that it is not realistic. 
  I have a problem with the calculation of the year and week combination when adding weeks or subtracting them. 
  The start data looks like this:</p>
  
  <pre><code>yyyyww (example: 201525, year 2015 week 25)
  </code></pre>
  
  <p>Now if I want to add for example 3 weeks, I can just do that by adding 3, results is 201528. However when it comes to 201552 (and sometimes yyyy53) it is more difficult as I need to calculate to 2016.</p>
  
  <p>The same goes for when calculating back in the time, towards 2014 or lower. Does anyone know or have a solution for this? Maybe in VBA? or a formula trick?</p>