Generally speaking, CET = UTC+1, and CEST = UTC+2. Though in some contexts, CET may be used to identify the pair. It's slightly different than the US, as we have the generic term Pacific Time to cover both PST and PDT, but Europe doesn’t have such a generic term. Looking at your implementation, may I suggest that you create a url for time.is/CEST that is always UTC+2, while time.is/CET is always UTC+1. However, you may want to add a link on the CET page that says something like, "Some locations that observe CET in the winter may be currently observing CEST". Keep in mind that while EU countries are aligned, other locations may use CET/CEST but transition on alternate dates or times, and other locations may be on CET all year long. Also consider that CLDR gives "Central European Standard Time" for long standard form, "Central European Summer Time" for the long daylight form, and "Central European Time" for the long generic form. However, it gives the abbreviations "CEST" to the short daylight form, and "CET" to both the short standard and short generic forms. http://www.unicode.org/cldr/charts/28/by_type/timezones.europe.html As you work more with other time zone abbreviations, you're going to find many other inconsistencies and ambiguities. CST having 5 different interpretations, etc. https://en.wikipedia.org/wiki/List_of_time_zone_abbreviations -----Original Message----- From: tz-bounces@iana.org [mailto:tz-bounces@iana.org] On Behalf Of Even Scharning Sent: Friday, October 23, 2015 11:52 AM To: Time Zone Mailing List <tz@iana.org> Subject: [tz] Official definition and origin of the term "Central European Time" Is there an official definition of the term "Central European Time" (CET), specifically which UTC offset(s) it refers to? If there is no official definition, where did the term originate from? I asked the information desk at the EU (Europe Direct) to help me find links to relevant legislature, but their reply was that term CET is "not regulated at a EU level, but internationally". All credible sources I have found, say that CET is a constant UTC+1. The closest thing I have found to an authoritative document, is the German Time Act from 1978. It says: "Legal time is Central European Time. It is defined as Coordinated Universal Time plus one hour." There is no reference to the origin of this definition, and no information of whether anyone other than the Germans agree on this definition. http://www.cl.cam.ac.uk/~mgk25/time/zeitgesetz.en.html On the EU's web pages (for instance http://europa.eu/contact/index_en.htm) times are usually given in CET, not CEST (Central European Summer Time), even though daylight saving time is currently observed. Google gives a few hundred thousand results for CET on europa.eu, and numerous of these results are hits on dates in the daylight saving time period. I think it makes more sense to define CET as alternating between UTC+1 (standard time) and UTC+2 (when DST is observed). (See http://time.is/CET for a more elaborate definition.) This is in line with for instance the US time zones Pacific Time and Eastern Time, which refer to the time currently observed, whether it is standard time or daylight saving time. Even Scharning Time.is - exact time for any time zone http://time.is/