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How to Use the World Clock
- View the default cities — The world clock starts with eight popular cities: London, New York, Tokyo, Sydney, Dubai, Los Angeles, Paris, and Singapore. Each card shows the current time, date, and UTC offset.
- Add a custom city — Use the "Add a city" dropdown at the top of the clock grid to search for any city or IANA time zone. Select the one you want and click the Add button to include it in your display.
- Check business hours — Cards with a green border indicate that the city is currently within standard business hours (9 AM to 6 PM local time), helping you determine the best time for calls or meetings.
- Remove a city — Click the X button in the top-right corner of any city card to remove it from your display. Your updated selection is saved automatically.
- Return anytime — Your selected cities are saved to your browser's localStorage, so they persist between visits without needing an account or sign-up.
How the World Clock Works
Our world clock uses the browser's built-in Intl (Internationalisation) API to convert your device's system time into the local time for each selected city. This API relies on the IANA time zone database, which is the same authoritative source used by operating systems and servers worldwide. It contains accurate rules for every time zone, including all historical and current daylight saving time transitions.
The clock updates every second using a JavaScript interval timer, ensuring that the displayed times are always current and synchronised with your device clock. Each card calculates its UTC offset dynamically by comparing the current time in UTC with the local time in the selected zone, which means the offset automatically adjusts when a city enters or exits daylight saving time.
Your city selections are persisted using the browser's localStorage API, which stores data locally on your device without sending anything to a server. This means your preferences are available across browser sessions but are specific to the browser and device you are using. Clearing your browser data will reset your selections to the default cities.
Frequently Asked Questions
How do I add more cities to the world clock?
Use the "Add a city" dropdown menu at the top of the clock grid. You can search through all IANA time zones and select any city. Click the Add button to include it in your display. Your selections are automatically saved to your browser's local storage, so they will still be there when you return.
Does the world clock update in real time?
Yes. The world clock updates every second using your device's system clock and the browser's built-in Intl API for accurate time zone conversion. The times shown are always live and reflect the current moment in each city, including any daylight saving time adjustments that are currently in effect.
How does the world clock handle daylight saving time?
The world clock uses the IANA time zone database built into your browser, which includes all current daylight saving time rules for every region. When a city transitions into or out of DST, the displayed time automatically adjusts. You do not need to do anything manually, as the browser handles all DST transitions.
Are my favourite cities saved between visits?
Yes. Your selected cities are stored in your browser's localStorage, so they persist between visits and page reloads. If you clear your browser data or use a different browser, you will start with the default set of cities. No account or sign-up is required to save your preferences.
What does the UTC offset mean?
The UTC offset shows how many hours ahead or behind a city is compared to Coordinated Universal Time (UTC). For example, UTC+5.5 means the city is five and a half hours ahead of UTC. This offset can change during daylight saving time transitions, which is why some cities show different offsets at different times of the year.
How many time zones are supported?
Our world clock supports every time zone in the IANA time zone database, which includes over 400 entries covering every inhabited region on Earth. This includes major cities, small territories, and historical time zones. You can add any of them using the dropdown selector above the clock grid.
