>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #2917145. --> Reported by: [gngn](https://www.drupal.org/user/1074656) Related to !79 >>> <ul> <li>I'm using a calendar view with month and week display</li> <li>month display is showing week numbers</li> <li>my system uses <em>monday</em> as <em>First day of week</em></li> <li>I am expecting to get ISO 8601 week numbers and years, e.g.: <ul> <li>2017-10-18: week 42, year 2017</li> <li>2017-01-02: week 01(!), year 2017</li> <li>2017-01-01: week 52, year 2016(!)</li> <li>2015-12-31: week 53, year 2015</li> <li>2016-01-01: week 53, year 2015</li> </ul> <p> (see <a href="http://php.net/manual/en/function.date.php">PHP date()</a>)</p></li> </ul> <p>With this setting there are some errors in the month display:</p> <ul> <li>The week numbers are off by one - i.e. 43 instead of 42 for 2017-10-18</li> <li>the first week links for <em>Januar 2017</em> (argument <em>201701</em>) have the arguments <em>20171</em>, <em>20172</em> instead of <em>2017<strong>0</strong>1</em>, <em>2017<strong>0</strong>2</em><br> (resulting in <em>Page not found</em>)</li> </ul> <p>There is no "Use ISO-8601 week numbers" or similiar in Configuration &gt; Regional and language &gt; Regional settings, so I think we should deliver ISO weeks if <em>First day of week</em> is set to <em>monday</em>.</p> <p>Proposed solution:</p> <ul> <li>Check if <em>First day of week</em> is set to <em>monday</em></li> <li>If so: use ISO 8601 week numbers and years</li> </ul> <p>Patch coming.</p>