[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fvxxkjzh1y1gj":3},{"_id":4,"slug":5,"title":6,"subtitle":7,"kind":8,"cards":9,"tags":57,"categories":59,"source":61,"lang":64,"author":65,"audioState":68,"stats":69,"publishedAt":72,"renderer":73},"6abc2ea3ca21c797c7e9e6f6","your-browser-timezone-and-your-ip-timezone-are-two-different-48979af1","Your browser timezone and your IP timezone are two different answers","Have you ever called Intl.DateTimeFormat().resolvedOptions().timeZone in your browser, compared it with an IP-geolocation-based \"my timezone\" result, and gotten two different answers?","news",[10,12,17,22,27,32,37,42,47,52],{"headline":6,"body":7,"imageUrl":11,"sourceImageUrl":11},"https:\u002F\u002Fmedia2.dev.to\u002Fdynamic\u002Fimage\u002Fwidth=1200,height=627,fit=cover,gravity=auto,format=auto\u002Fhttps%3A%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Farticles%2Fyfmyw4tu2vhvoe26rqrp.png",{"headline":13,"body":14,"imageUrl":15,"images":16},"Neither answer is wrong. They answer two different","Neither answer is wrong. They answer two different questions. Here is how they differ, why a mismatch is usually normal, and why a bare UTC offset is never enough to define a timezone. Your browser timezone: what your OS claims When JavaScript asks for your time zone, it doesn't ask the network — it asks the operating system:","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F1.webp",{"local":15},{"headline":18,"body":19,"imageUrl":20,"images":21},"Intl.DateTimeFormat().resolvedOptions().timeZone returns an IANA time zone…","Intl.DateTimeFormat().resolvedOptions().timeZone returns an IANA time zone identifier (like Asia\u002FShanghai, America\u002FNew_York, or Europe\u002FBerlin) taken from the OS settings. It is free, instant, and privacy-friendly — but only as accurate as the machine's own configuration. Your IP timezone: what your exit IP suggests","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F2.webp",{"local":20},{"headline":23,"body":24,"imageUrl":25,"images":26},"An \"IP timezone\" is estimated from your egress","An \"IP timezone\" is estimated from your egress IP address via a GeoIP database. It answers a completely different question: where does the internet think your connection comes out? These two can legitimately disagree:","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F3.webp",{"local":25},{"headline":28,"body":29,"imageUrl":30,"images":31},"VPN \u002F proxy \u002F corporate egress — your","VPN \u002F proxy \u002F corporate egress — your browser reports Asia\u002FTaipei, but your traffic exits in Frankfurt, so the IP-based estimate says Europe\u002FBerlin. Remote desktop \u002F cloud VM — the OS belongs to a machine on another continent. Manually changed system timezone — developers do this all the time to test scheduling logic. Stale or coarse GeoIP data — IP-to-location mappings are estimates, and they shift.","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F4.webp",{"local":30},{"headline":33,"body":34,"imageUrl":35,"images":36},"So when the two answers differ, it is","So when the two answers differ, it is not necessarily a bug on either side. It is a signal worth understanding — especially if your app relies on it for scheduling, logging, or analytics. UTC offset ≠ time zone identifier","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F5.webp",{"local":35},{"headline":38,"body":39,"imageUrl":40,"images":41},"This is the part that bites developers most","This is the part that bites developers most often. An offset like \"UTC+8\" is a snapshot, not an identity. \"How many hours apart are two time zones?\" is a question that only makes sense with a date attached, because daylight saving time shifts offsets through the year. Take America\u002FNew_York: it is UTC-5 in January and UTC-4 in July. Hard-coding -5 will be wrong for half the year. And the three-letter abbreviations are a trap. CST can mean at least three different things: China Standard Time — UTC+8, no DST, all year US Central Standard Time — UTC-6, switching to CDT (UTC-5) in summer Cuba Standard Time — UTC-5, with its own DST rules","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F6.webp",{"local":40},{"headline":43,"body":44,"imageUrl":45,"images":46},"\"PST\" is no better (US Pacific vs. Philippine","\"PST\" is no better (US Pacific vs. Philippine Standard Time, which is UTC+8 and observes no DST). Always use IANA identifiers like Asia\u002FShanghai or America\u002FChicago in code, APIs, and databases — never bare abbreviations. A free tool that makes all of this visible","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F7.webp",{"local":45},{"headline":48,"body":49,"imageUrl":50,"images":51},"I came across a free timezone tool that","I came across a free timezone tool that puts these concepts into practice. Everything is computed locally in the browser — no location permission prompts, no data uploaded:","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F8.webp",{"local":50},{"headline":53,"body":54,"imageUrl":55,"images":56},"Browser timezone, instantly — shows the IANA identifier","Browser timezone, instantly — shows the IANA identifier your browser reports, the current UTC offset, and whether DST is active.","\u002Fapi\u002Fmedia\u002Fposts\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-48979af1\u002F9.webp",{"local":55},[58],"dev",[60],"Technology",{"name":62,"url":63},"Dev.to","https:\u002F\u002Fdev.to\u002Fgraysally223\u002Fyour-browser-timezone-and-your-ip-timezone-are-two-different-answers-1jem","en",{"handle":66,"displayName":67},"spots","Spots","queued",{"views":70,"likes":71,"saves":71,"shares":71,"completions":71,"opens":71,"skips":71,"depthSum":71},3,0,"2026-09-29T21:33:23.699Z","local"]