What the Digital Clock does
This is a large, full-screen digital clock for your browser. It shows the current time with seconds and the date in 12- or 24-hour format, in your own time zone or any other, with a dimmed night look for a bedside or a dark room, and a row of world clocks that tells you how far ahead or behind each city is.
It can also keep your screen from going to sleep while the tab is open, using the browser's Screen Wake Lock, so a spare phone, tablet or monitor becomes a desk or wall clock. The time comes from your own device; nothing is sent anywhere.
How to use it
- Choose 12-hour or 24-hour time. The page starts with whichever your device uses.
- Pick a time zone if you want a clock for somewhere else - UTC for flight or server times, or a city where colleagues or family live.
- Choose the night look for a dark room, and switch seconds or the date on or off.
- Add world clocks for other cities. Each card shows that city's time, whether it is already tomorrow or still yesterday there, and the difference from your main clock.
- Press Full screen to fill the display, and tick "Keep the screen awake" if the device would otherwise dim. Press Escape or Exit full screen to return.
Reading the results
The offset under the clock, such as UTC+5:30 or UTC-4, is how far that zone is from Coordinated Universal Time at this moment. It changes by an hour in places that use daylight saving time, and the clock follows those changes automatically.
World-clock differences are measured from the zone of the main clock. "4 h 30 min ahead" for Kolkata seen from London is true in summer; in winter, when London moves back to UTC+0, it becomes 5 h 30 min.
"Tomorrow" or "yesterday" on a card means that city's calendar date differs from the main clock's, which is common between Asia, Europe and the Americas in the evening and early morning.
Worked example: an office world clock
At 13:05:09 UTC on Tuesday 20 October 2026, a main clock in London reads 14:05:09 - London is on British Summer Time, UTC+1.
The world row shows Los Angeles at 06:05 (8 h behind), New York at 09:05 (5 h behind), Dubai at 17:05 (3 h ahead), Kolkata at 18:35 (4 h 30 min ahead), Singapore at 21:05 (7 h ahead) and Sydney at 00:05 on Wednesday - already tomorrow, 10 h ahead, because Sydney is on daylight time (UTC+11) in October.
After 25 October, when London returns to UTC+0, the same row shows New York 4 h behind until the US clocks change a week later on 1 November - the kind of shift that catches out meeting invitations, and which the clock handles from the browser's time-zone rules.
How accurate is a browser clock?
The clock reads your device's own time every second, and most phones and computers set that automatically from network time servers, so it is normally within a fraction of a second. The page does not count seconds itself: each tick reads the real time again, and ticks are lined up with the start of each second. When the tab has been in the background - where browsers slow timers down - it shows the correct time the moment you come back.
Time-zone rules, including daylight-saving dates, come from the IANA time zone database built into your browser. That is why half-hour and quarter-hour zones such as India (UTC+5:30) and Nepal (UTC+5:45) are shown correctly without any manual offsets.
Keeping the screen on
The Screen Wake Lock API lets a page ask the device not to dim or lock the screen. This page asks only when you tick the box, and only while the tab is visible; the browser releases the lock as soon as you switch tabs, and the page asks again when you return. Some browsers and battery-saver modes refuse the request, and the page tells you when that happens - in that case change the device's display sleep setting instead.
Limitations: what the result does not prove
- The clock is only as correct as your device's time. If your device clock is set by hand and has drifted, the page shows that drift.
- It is a display, not an alarm: it makes no sound. Use an alarm or timer page, or your phone's clock app, for something that must wake you.
- Keeping the screen awake uses more battery, and it only works while the tab is open and visible.
- Very old browsers may lack the full list of time zones; the page falls back to a list of major cities.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- W3C - Screen Wake Lock API
- IANA - Time Zone Database
- MDN - Intl.DateTimeFormat (time zones in the browser)
Frequently asked questions
How do I show a full-screen clock on my computer?
Press Full screen under the clock. It fills the whole display with large digits; choose the night look for a dark room. Press Escape or Exit full screen to return. On a phone, rotate to landscape for the biggest digits.
How do I switch the clock between 12-hour and 24-hour time?
Use the Format switch. 12-hour time shows 1 to 12 with AM or PM - midnight is 12:00 AM and noon is 12:00 PM. 24-hour time runs from 00:00 to 23:59, as used in timetables and most of Europe and India.
Can I see the time in other cities at the same time?
Yes. Add world clocks from the list - up to 12. Each card shows the city's time, how many hours it is ahead or behind your main clock, and whether its date is already tomorrow or still yesterday.
Will the clock stop my screen from turning off?
Tick "Keep the screen awake". Where the browser supports the Screen Wake Lock API, the screen stays on while this tab is visible. It is released automatically when you switch away, and the page says so if your browser or battery saver refuses.
Does the clock change automatically for daylight saving time?
Yes. The time and the offset come from the time-zone database in your browser, so when London, New York or Sydney change their clocks, the main clock and every world clock change with them at the right moment.
Can I use an old phone or tablet as a desk clock?
Yes - open this page, choose full screen and the night look, and tick keep the screen awake. Leave the device on its charger, since an always-on screen uses battery. The clock keeps correct time from the device.
Last reviewed by the A2Z.Tools team against the sources listed above.
