It's National Cat Day on December 15th.
More on Cat Day and the other days on the 15th below.
The day shown for 'National Cat Day' is shown as we detected that day mentioned the most out of all the references to national days there were on December the 15th across social media. Our algorithms examine all of the references to National Days across social media and updates whatnationaldayisit.com hourly, with our homepage displaying the current national day. This crowdsourcing of data method to assess the National Day date is used as opposed to being connected with any Government sacntioned lists :D Hurrah for democracy by concensus!