Bizarre.  The author seems to be implying that only one definition of the first day of a week can be tolerated (and that his is implicitly the correct one), and later in the comments field that it&#x27;s intolerable that the 1st of January could ever not be in the first week of a given year.<p>ISO8601 [1] is pretty clear on how you determine the first week (as noted on the wikipedia page, these are functionally equivalent) :<p>o the week with the year&#x27;s first Thursday in it (the formal ISO definition),<p>o the week with 4 January in it,<p>o the first week with the majority (four or more) of its days in the starting year, and<p>o the week starting with the Monday in the period 29 December – 4 January.<p>While it&#x27;s doubtless fun to scream into the wind (of International Standards), and perhaps we may churlishly expect MS to instinctively resist anything labelled as a standard, comments like this:<p><pre><code>  &gt; The customer wants to know if there is anything we can do so we
  &gt; get the correct result. 
</code></pre>
are somewhat distressing.<p>The customer already has the correct result, just neither party understands what the correct result should be.<p>[1] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;ISO_8601" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;ISO_8601</a>