Websites determine your timezone through two methods: IP geolocation (which maps your IP address to a timezone region) and the browser's built-in JavaScript API, which reads your device's configured timezone directly. You can see which timezone your connection is associated with on whatsmy.fyi.
Method 1: IP-Based Timezone Detection
IP geolocation databases include timezone data alongside city and country information. Every IP address is mapped to a timezone based on the geographic region where it is allocated. For example, an IP in Istanbul would map to Europe/Istanbul, and an IP in New York would map to America/New_York.
Cloudflare provides the cf.timezone field in its request context β the timezone associated with your IP's geolocation. This is how whatsmy.fyi reads your network timezone: directly from Cloudflare's edge data, with no external API call.
Method 2: JavaScript Intl API
The JavaScript Intl.DateTimeFormat API allows the browser to read your device's configured timezone:
Intl.DateTimeFormat().resolvedOptions().timeZone
// β "Europe/Istanbul"This is the timezone your operating system is set to β not necessarily where you are physically located. If you have a VPN active and your IP geolocates to Germany, but your device is set to America/New_York, the JavaScript API will return the American timezone regardless of your IP.
This discrepancy between IP timezone and browser timezone is one of the signals that fraud detection systems use to identify VPN users or users with inconsistent location signals.
What Is a Timezone Identifier?
Timezone identifiers (like Europe/Istanbul or America/Los_Angeles) are part of the IANA (Internet Assigned Numbers Authority) Time Zone Database, also called the Olson database. They are geographic names rather than UTC offsets, because UTC offsets change with daylight saving time (DST).
For example, America/New_York is UTC-5 in winter (Eastern Standard Time) and UTC-4 in summer (Eastern Daylight Time). Using the full IANA identifier ensures correct time conversion regardless of DST.
UTC and UTC Offsets
UTC (Coordinated Universal Time) is the primary time standard to which all timezones are expressed as offsets. The UTC offset for a timezone tells you how many hours and minutes ahead or behind UTC it currently is:
Europe/Istanbulβ UTC+3 (no DST)America/New_Yorkβ UTC-5 (winter) / UTC-4 (summer)Asia/Tokyoβ UTC+9 (no DST)Pacific/Aucklandβ UTC+12 (winter) / UTC+13 (summer)
whatsmy.fyi shows both the IANA timezone identifier and the current UTC offset, calculated in real time.
Why Does Timezone Detection Matter?
Timezone data is used for:
- Scheduling and event localisation: Calendar apps, meeting schedulers, and ticketing platforms use your timezone to show times correctly.
- Content personalisation: Publishing "today's news" based on what day it is in your timezone.
- Fraud detection: Comparing your IP-derived timezone against your browser timezone as one of many consistency signals.
- Legal and compliance: Some services have different content or pricing rules based on your timezone/jurisdiction.
Frequently Asked Questions
Can I hide my timezone from websites?
You can change your browser's reported timezone using developer tools or browser extensions. Firefox allows you to override it with privacy.resistFingerprinting. However, changing your timezone without changing your IP can increase inconsistency signals that fraud detection systems look for.
Why does whatsmy.fyi show a different timezone than my device?
whatsmy.fyi shows the timezone derived from your IP address geolocation (from Cloudflare). This is the timezone your IP is associated with, which may differ from your device's configured timezone β especially if you are using a VPN or if you are travelling.
What is the difference between a timezone and a UTC offset?
A UTC offset (e.g., UTC+3) is a fixed number β it does not account for daylight saving time. A timezone identifier (e.g., Europe/Istanbul) encodes the full history of offset changes for a region, including DST transitions. Always use IANA timezone identifiers for reliable time calculations.
