What is my timezone?

How your browser knows your timezone

Your browser asks the operating system, which knows the timezone you selected during setup or that was chosen for you by location services. The value is exposed through Intl.DateTimeFormat().resolvedOptions().timeZone and is reported as an IANA identifier — a Region/City name such as Europe/Berlin.

Crucially, this has nothing to do with your IP address. The two are independent signals, which is why comparing them is such a reliable way to spot a VPN.

Why offsets are not timezones

An offset is a snapshot; a timezone is a rulebook. America/New_York is UTC−05:00 in January and UTC−04:00 in July, and the exact transition dates have changed several times by legislation. Storing -05:00 throws away everything needed to compute the next transition correctly.

The practical rule for developers: store timestamps in UTC, store the user's IANA timezone name separately, and convert only at display time. Storing local time with an offset is the root of a large share of scheduling bugs.

Daylight saving time

Roughly a third of the world observes daylight saving, on dates that vary by country and change by legislation more often than most people expect. The IANA timezone database tracks all of it and ships updates several times a year — which is why keeping that database current matters on any system that handles scheduling.

Timezone as a fingerprinting signal

Timezone is a modest but useful fingerprinting input: it narrows a visitor to one of a few dozen populated regions. Its real value to trackers is cross-checking — a connection from a Dutch IP address whose browser reports Asia/Baghdad is visibly proxied.

Everything on this page is read in your browser and displayed directly. Nothing is sent to our servers. See the full list of what your browser exposes on the browser info page.

When your browser timezone and your IP disagree

These two values come from completely different places, and comparing them is more informative than either alone. The timezone above is read from your own operating system's setting. The timezone an IP lookup reports is inferred from the estimated location of your address in a geolocation database.

A mismatch is not an error, and it usually has an ordinary explanation: you are using a VPN and the exit server is elsewhere; you are travelling and your laptop clock has not been changed; your corporate network routes through another country; or the geolocation database is simply wrong about your city, which is the field it is least reliable about. Fraud-detection systems look at exactly this mismatch, which is why a VPN sometimes triggers additional verification on banking sites.

Why applications should store IANA names, not offsets

An offset such as UTC+02:00 describes a moment, not a place. Storing it and reusing it later produces bugs the first time daylight saving changes, because the same location has a different offset in July than in January.

An IANA identifier such as Europe/Istanbul or America/Sao_Paulo describes the place and carries its entire history of rule changes. That matters more than it sounds: Türkiye stopped changing clocks in 2016, Brazil abolished daylight saving in 2019, and any system that hard-coded their offsets was wrong the following season. The identifier is what your browser exposes here, and it is what you should store.