This script gives you the zone info key representing your device's time zone setting.

The return value is an IANA zone info key (aka the Olson time zone database).

The IANA timezone database is pretty much standard for most platforms (UNIX and Mac support it natively, and every programming language in the world either has native support or well maintained libraries that support it).

Example Use

Invoke the script by calling

    var tz = jstz.determine();

Use Case

The script is useful if you do not want to disturb your users with questions about what time zone they are in. You can rely on this script to give you a key that is usable for server side date and time normalizations across time zones.


This script does not do geo-location, nor does it care very much about historical time zones. So if you are unhappy with the time zone "Europe/Berlin" when the user is in fact in "Europe/Stockholm" - this script is not for you. They are both identical in modern time.

Also, if it is important to you to know that in Europe/Simferopool (Ukraine) the UTC offset before 1924 was +2.67, sorry, this script will not help you.

Time zones are a screwed up thing, generally speaking, and the scope of this script is to solve problems concerning modern time zones, in this case from 2010 and onwards.

Web Implementation

Simply include the dist/jstz.min.js file on your webpage at which point the jstz object will be exposed to you

NPM package

The latest version is always available as jstimezonedetect in NPM.

    > var jstz = require('jstimezonedetect');
    > jstz.determine().name();


There is an updated demo running on: http://pellepim.bitbucket.org/jstz/.


If you want to contribute to the project (perhaps fix a bug, or reflect a change in time zone rules), please simply issue a Pull Request. Please take note that jstz.main.js is the source code, while jstz.rules.js is a generated file which, any changes therein will be overwritten. The build is found in the dist folder in full and minified versions.


Thanks to

Other contributors: Gilmore Davidson