Determine a user's timezone

Question

Is there a standard way for a web server to be able to determine a user's timezone within a web page?

Perhaps from an HTTP header or part of the user-agent string?

Solution 1

-new Date().getTimezoneOffset()/60;

The method getTimezoneOffset() will subtract your time from GMT and return the number of minutes. So if you live in GMT-8, it will return 480.

To put this into hours, divide by 60. Also, notice that the sign is the opposite of what you need - it's calculating GMT's offset from your time zone, not your time zone's offset from GMT. To fix this, simply multiply by -1.

Also note that w3school says:

The returned value is not a constant, because of the practice of using Daylight Saving Time.

Solution 2

The most popular (==standard?) way of determining the time zone I've seen around is simply asking the users themselves. If your website requires subscription, this could be saved in the users' profile data. For anon users, the dates could be displayed as UTC or GMT or some such.

I'm not trying to be a smart aleck. It's just that sometimes some problems have finer solutions outside of any programming context.

Solution 3

There are no HTTP headers that will report the clients timezone so far although it has been suggested to include it in the HTTP specification.

If it was me, I would probably try to fetch the timezone using clientside JavaScript and then submit it to the server using Ajax or something.

Solution 4

First, understand that time zone detection in JavaScript is imperfect. You can get the local time zone offset for a particular date and time using getTimezoneOffset on an instance of the Date object, but that's not quite the same as a full IANA time zone like America/Los_Angeles.

There are some options that can work though:

• Most modern browsers support IANA time zones in their implementation of the ECMAScript Internationalization API, so you can do this:

const tzid = Intl.DateTimeFormat().resolvedOptions().timeZone;
console.log(tzid);

The result is a string containing the IANA time zone setting of the computer where the code is running.

Supported environments are listed in the Intl compatibility table. Expand the DateTimeFormat section, and look at the feature named resolvedOptions().timeZone defaults to the host environment.

• Some libraries, such as Luxon use this API to determine the time zone through functions like luxon.Settings.defaultZoneName.

• If you need to support an wider set of environments, such as older web browsers, you can use a library to make an educated guess at the time zone. They work by first trying the Intl API if it's available, and when it's not available, they interrogate the getTimezoneOffset function of the Date object, for several different points in time, using the results to choose an appropriate time zone from an internal data set.

  Both jsTimezoneDetect and moment-timezone have this functionality.

    // using jsTimeZoneDetect
    var tzid = jstz.determine().name();
  
    // using moment-timezone
    var tzid = moment.tz.guess();
  

  In both cases, the result can only be thought of as a guess. The guess may be correct in many cases, but not all of them.

  Additionally, these libraries have to be periodically updated to counteract the fact that many older JavaScript implementations are only aware of the current daylight saving time rule for their local time zone. More details on that here.

Ultimately, a better approach is to actually ask your user for their time zone. Provide a setting that they can change. You can use one of the above options to choose a default setting, but don't make it impossible to deviate from that in your app.

There's also the entirely different approach of not relying on the time zone setting of the user's computer at all. Instead, if you can gather latitude and longitude coordinates, you can resolve those to a time zone using one of these methods. This works well on mobile devices.

Solution 5

JavaScript is the easiest way to get the client's local time. I would suggest using an XMLHttpRequest to send back the local time, and if that fails, fall back to the timezone detected based on their IP address.

As far as geolocation, I've used MaxMind GeoIP on several projects and it works well, though I'm not sure if they provide timezone data. It's a service you pay for and they provide monthly updates to your database. They provide wrappers in several web languages.

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Comments

[bimbom22]

this is what makes the most sense to me. is there any reason this shouldn't be used or is everyone above just making the problem more difficult than they need to.

[JD Isaacks]

@jordanstephens I am not an expert so I do not know if there are circumstances where this would not work, but it worked fine for me.

[Marcy Sutton]

What about when a user is downloading an .ics file that should have a start time specific to their location (e.g. 9-11am across the country)? They shouldn't HAVE to say what their time zone is imo.

[Lenik]

Why not accept this as the correct answer? The answer given by Unkwntech even not work for non-IE browsers.

[Rajat Gupta]

@Ishmaeel: but users do travel internationally and they shouldnt need to tell their timezone each time they login from some non-native timezone

[G-Wiz]

This doesn't answer the question, which clearly implies he's looking for a technological solution.

[Nischal]

What about users who use cell phones that have browsers without javascript support? I like the question, the user asks about HTTP headers, user agent... is there a way to make this work server side, as accurate as possible?

[Christopher Chase]

i do like this, but i might have something that checks the current $_SESSION['time'] and only get the javascript to reload if its different

[Peter O.]

I have voted this answer up because the latitude and longitude obtained from databases like GeoIP (which has a free version available as of now) can be combined with databases that convert such a coordinate to a time zone. I think GeoNames has a latter such database.

[hippietrail]

That's strange. For me this returns -4 but I'm in GET which ought to be +4 - what am I missing? I've checked that my OS is set to the correct timezone.

[NudeCanalTroll]

getTimezoneOffset() returns number of minutes when you subtract your current time from GMT time. So if you live in California, that's PST, which is GMT-8, so you're 8 hours behind. Subtract that from GMT using getTimezoneOffset(), and it will return 480 minutes. If you want to find your offset, multiply that by -1 and divide by 60.

[chown]

Why did you repost an identical answer (by John Isaacks) from 2 years ago: stackoverflow.com/a/1809974/836407 ?

[Simon Bergot]

@gWiz OP is asking for a standard solution. This is pretty standard.

[arlomedia]

This worked for me! Read the comments under the blog post for a couple updates to the code.

[arlomedia]

This doesn't account for Daylight Saving Time / Summer Time, but the link posted by Joseph Lust does: stackoverflow.com/a/5492192/462162

[Benbob]

This doesn't always work for DST. Get timezone offset does exactly what it says. It get's the offset. A time ZONE is actually a geographical area. This won't work for daylight savings since you don't know which hemisphere the user lives in, or if their country even has daylight savings. Why not use this instead: >>> date.toTimeString() "15:46:04 GMT+1200 (New Zealand Standard Time)"

[Gan]

The link is dead. I think this is the alternative link: devproconnections.com/article/aspnet2/it-s-about-time-122778

[Ivaylo Slavov]

The article is available as PDF form here too: app.box.com/shared/bfvvmidtyg

[xgretsch]

I beg to differ with Keyo. The definition of getTimezoneOffset() (according to the ECMA standard ecma-international.org/ecma-262/5.1/#sec-15.9.5.26) is "Returns the difference between local time and UTC time in minutes." - in other words, it should take daylight savings into account. Mozilla's documentation says "Daylight saving time prevents this value from being a constant even for a given locale."

[Mike Dimmick]

@xgretsch: It gets the user's current offset from GMT. That's fine if you're presenting another time that occurs on the same day (unless the current date is a changeover date, where it could be wrong). However, there are many timezones which have the same offset from GMT, and they may have different changeover dates or not use daylight savings.

[Mike Dimmick]

@Keyo: toTimeString's output is implementation-defined: ecma-international.org/ecma-262/5.1/#sec-15.9.5.4. There is no guarantee that it will include a time zone name. There is also no guarantee that if it does include a time zone name, that it maps to anything the server knows about. It may work in some browsers some of the time, but I wouldn't like to rely on it.

[sovemp]

@Mike Dimmick: While true, the question itself asks if there is a way to get the time zone offset, not the actual time zone itself, so this should be correct.

[xgretsch]

@Mike Dimmick: Ah, I see your point. I guess there isn't a simple answer to "what's the user's time zone offset" - you need to ask "what's the user's time zone offset at a particular point in time". I'm beginning to think that the only robust way of doing this is one of those horrible solutions where you set the time zone, print out the time in local time, and compare what you got!

[Matt Johnson-Pint]

Also, it only returns the current time zone offset - not the time zone. See the timezone tag wiki.

[Matt Johnson-Pint]

Also, it only returns the current time zone offset - not the time zone. See the timezone tag wiki.

[Matt Johnson-Pint]

This only returns the current time zone offset - not the time zone. See the timezone tag wiki.

[Matt Johnson-Pint]

This will still only return the standard offset for the time zone, such as +02:00. It will not give you enough information to determine the time zone of the user, such as Africa/Johannesburg or Europe/Istanbul. See the timezone tag wiki.

[Jason Walton]

One thing to note here; some places (such as Newfoundland in Canada) have timezones that are off by half an hour, so after dividing by 60 your answer may not be an integer.

[ingredient_15939]

To solve the above, why not get the browser's current time (ie. actual time, not offset) then, server-side, determine GMT offset by comparing browser's current time with server's current time (assuming you know the server's own GMT offset). This seems the least problematic solution to me. You can determine the time zone from there. In .NET, for example, you can use TimeZoneInfo to cycle through current times in each zone, until a match is found for the browser's reported time (or query an online time service).

[Stephen Blair]

The method of converting UTC server time to local client time described in this article is wrong. Using the current client offset to adjust UTC times on the server will result in incorrect "local" times for half the year for client locales that observe daylight savings time. Consider this scenario: a client in the UK on 14 Jan 2013 (GMT+0000 Standard Time) sets a date and time of 21 Aug 2015 14:00 (GMT+0100 Daylight Time). This gets normalised on the server to 21 Aug 2015 13:00 UTC. On the day this occurs the client offset is 0 so the time sent back to the client will be 21 Aug 2015 13:00.

[Alek Davis]

Valid point, but I didn't claim this to be a bullet-proof solution. If you need to implement a really time-sensitive solution, say a train ticket booking application, then you need to find a more comprehensive (and complex solution). However, for many apps this would not be an issue. Because in many cases we want to localize GMT values for current session. Now, if you have an application that needs to save a time stamp for some even in the future and it cannot tolerate DTS, then a proper way would be to present an option to save time directly in GMT. If you know a better option, please share.

[IMSoP]

Link only answers are discouraged, because if the link disappears, the answer ceases to be useful; and because without following the link, readers don't know whether it gives a good answer. In this case, you could clarify that this is a 3rd-party library which takes a database-based approach to identification, and maybe explain some of the principles of its operation.

[IMSoP]

It's probably easier to use a Cookie than a Session to transport this, since locking and unserializing the PHP session may cause slowdowns in your app. For maximum efficiency, you could copy the value into the session and delete the cookie so that it's not sent in subsequent requests.

[IMSoP]

This doesn't account for "daylight saving" adjustments - a user in Dublin would match your 'Europe/Dublin' in winter, but 'Europe/Belgrade' in summer. If you're going to use the current offset, all you can reasonably assume is that offset, not a geographical identifier.

[IMSoP]

Unfortunately, that header seems to be mainly designed for responses, not requests: "A user agent MAY send a Date header field in a request, though generally will not do so unless it is believed to convey useful information to the server." I just checked, and Firefox does not send it.

[Triynko]

The user's computer clock could be wrong, in which case this would fail. For example, if I'm serving a report to teachers that lists student responses to questions with their times, and my database stores times in UTC, then I would need to know a time-zone offset, and the user's current computer time would be irrelevant. The only way to reliably obtain such an offset would be to either ask the user (i.e. ensure the time zone is included with report request, or add a drop down for time-zone above the report and do the conversion client-side), or determine the user's physical location via GPS.

[Triynko]

The best solution would probably be a combination of asking the user (e.g. providing a time-zone drop down at the top of a report), while defaulting the drop down selection to a GPS-determined time-zone when the user is on a mobile device that provides location information, and otherwise default to UTC.

[Matthew Slyman]

The current versions (both free and paid-for) of the MaxMind GeoIP databases/ APIs, do indeed supply timezone information (it returns "Europe/London" for my timezone.) I can't remember whether the old version of their GeoIP system did the same, but it works very well now! The MaxMind fields are named "time_zone", "time_zone_name".

[TTT]

Strangely, this is the only correct answer to the question, which asks how to do it server side. I suspect the reason there are other answers with more votes is because once you realize you need to do it client side you end up using the other answers. But IMHO anyone upvoting another answer should be upvoting this one too.

[Rob]

The question asks how to determine it on the server side. This is code for the client.

[Pascal]

@user01 You can not make such a general statement and think it is correct for all situations. There are enough applications with user profile where the user is not travelling each day. Thus a dropdown with timezones to choose from is fine for "most" user requirements.

[Admin]

$unix_timestamp_ofshiz ? Something is missing here and doesn't quite work ,even though this seems like it could be a good answer.

[Kishor Pawar]

w3scool says The returned value is not a constant, because of the practice of using Daylight Saving Time. as a Note.

[Dirbaio]

This! This is the way to go. Simple library, handles DST properly. Other answers are full of WTF and many don't do DST.

[Mikko Rantalainen]

I believe the best method is to use geo-ip location to sort the possible time zones and by default pick the first one that is (close) match to user agent time offset (JavaScript required). Even after that, you have to provide a way to fix the timezone after even this method will select the incorrect one.

[philfreo]

Edited to include info about doing the same for the time zone name.

[Matthieu]

@MikkoRantalainen careful when using proxies through, as they don't always advertise themselves in the headers.

[Mikko Rantalainen]

This library is very clever. It works by querying current offset to UTC, then adjusting JavaScript Date object time by adding or substracting seconds until offset to UTC changes. Using this method this library figures out many enough DST changes to uniquely identify the timezone. I think the library could have even better performance if it did binary search instead of linear search. The return value is an IANA zone info key (aka the Olson time zone database).

[Mikko Rantalainen]

@Matthieu there exists a better answer nowadays: stackoverflow.com/a/11836123/334451

[Rambatino]

This is a just a copy of the accepted answer, why you even voting on it.

[Michael Tsang]

I think a simpler process is to call Intl.DateTimeFormat().resolvedOptions().timeZone and send it to web server. Ref: stackoverflow.com/questions/9772955/…

[Dan Dascalescu]

This library is no longer needed. Modern browsers support the Intl API, which returns the IANA timezone string. See this answer.

[Dan Dascalescu]

Nowadays, moment.js i no longer recommended. There are far smaller alternatives currently (dayjs, date-fns). Moment is huge.

[lscoughlin]

This doesn't even BEGIN to answer the question.

[lscoughlin]

This is literally the only answer that actually addressed the question posed.

[RobG]

Using the user's geographic location (i.e. their locale) to deduce the timezone is also flawed. Users may wish to use a specific timezone on their device that is not the local timezone, even thought it might display the same time (or not). E.g. travellers frequently leave their devices with the timezone set to their usual locality and do not expect to see dates and times use a different offset without being advised. I might be talking from personal experience here… ;-)

[Matt Johnson-Pint]

Can't tell if you're trolling me Rob. ;) But none of these approaches use their locale, but rather the setting on the device, so aligns with your point. (Only the alternate approach mentioned in the last paragraph would use current location.)

[azernik]

Chiming in with a terminology note: "locale" is emphatically not the user's geographic location. "Locale" is a group of settings such as language, number format, calendar, etc. For example, the de_DE locale specifies German as default language, the euro as default currency, commas as decimal separator, periods as the thousands separator, and Gregorian as the calendar. See developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

[Daniel Rodríguez Meza]

Great answer!, thank you

[FreeSoftwareServers]

Just want to say jsTimeZoneDetect came back wrong for me, but moment didn't! +1