Which time zone does the large clock use?

Your device's own zone, as your browser reports it, until you move one of your city clocks into the hero. The heading on the clock names what is shown: beneath the time on the digital panel, on the face itself on the dial.

Why does a city's offset read differently in summer and winter?

Because the clock asks the time-zone data for the offset at the instant it is showing. New York reads UTC−5 at the page's fixed January instant and UTC−4 at its fixed July instant, while Tokyo reads UTC+9 at both.

Why do some offsets show minutes?

Because the zone's offset is not a whole number of hours and the label keeps the minutes: at the January instant New Delhi reads UTC+5:30 and Kathmandu reads UTC+5:45.

Your city list, the 12/24 choice, the hero clock and the face you picked are kept in this browser's storage and are not transmitted. The clock asks the site's own time server for a timestamp to check this device's clock; that request carries no typed input. The place finder loads its place index from this site when you first search or browse.

Does the clock keep running while the tab is in the background?

Nothing runs while the tab is closed. While it is open, the page formats the current instant once a second, and on your return the next tick formats the instant then, so nothing has to catch up. The tools that sound a cue hold to the same line on their displays — correct whenever a tick runs — but whether the cue sounds depends on the device staying awake and the tab staying open, for every one of them. The alarm also keeps no stored envelope: the pomodoro, speech, interval and countdown timers resume from saved epochs after a reload, while a reload brings back the alarm page with nothing set.

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UTC

How this clock works

What the world clock shows, how each city's time is produced from one instant, and where the site stops — with every figure computed when the site was built.

What the clock shows

The page opens on one large clock and a row of smaller ones. The large clock is your local time by default — the heading on the clock names it — and it has two faces. The digital panel shows hours, minutes and seconds, the weekday and full date, and the zone’s offset from UTC, with the heading beneath the time. The analog dial shows hour, minute and second hands, and carries the heading and the short zone label on its face. The 12/24 switch in the header changes the hour format for every clock on the page. Under either face, a status line reports whether this device’s clock has been checked against the site’s own time server.

Below the hero sit the finder, the grid of city cards — each with a small two-handed face, the city and country, the time and the offset — and the strip of links to the 8 tools. Every figure in this section was produced by the engine’s own rules when the site was built, from fixed instants declared in its source.

How each city’s time is computed

Once a second the page takes the current instant from this device’s clock — adjusted, once the site’s own time server has answered, by the measured difference between the two — and formats it, separately, for every zone on screen; there is no arithmetic on a remembered difference between cities. The engine’s time formatter hands the instant and the city’s IANA zone identifier to the browser’s own date formatting, in the en-US locale, and asks for a numeric hour, a two-digit minute and a two-digit second, in 12-hour or 24-hour form according to the switch. The date formatter asks for the long weekday, month, day and year. The table runs the 6 default cities through the time formatter at one fixed instant, 09:00:00 UTC on Wednesday, January 14, 2026, a constant in this page’s source.

City	Zone	12-hour	24-hour	Offset
New York	`America/New_York`	`4:00:00 AM`	`04:00:00`	`UTC−5`
Los Angeles	`America/Los_Angeles`	`1:00:00 AM`	`01:00:00`	`UTC−8`
London	`Europe/London`	`9:00:00 AM`	`09:00:00`	`UTC`
Tokyo	`Asia/Tokyo`	`6:00:00 PM`	`18:00:00`	`UTC+9`
Sydney	`Australia/Sydney`	`8:00:00 PM`	`20:00:00`	`UTC+11`
Singapore	`Asia/Singapore`	`5:00:00 PM`	`17:00:00`	`UTC+8`

The two hour forms are not one string with a suffix — compare 4:00:00 AM with 04:00:00 for New York. And the date is formatted in the city’s zone, not yours. At this instant all 6 happen to share Wednesday, January 14, 2026; move the instant to 23:00:00 UTC on Wednesday, January 14, 2026 and the same cities split: New York, Los Angeles and London on Wednesday, January 14, 2026, Tokyo, Sydney and Singapore on Thursday, January 15, 2026.

Offsets, and the comparison rule

The offset on each card is computed too. The engine asks the formatter for the zone’s long offset name at the instant in question and parses the sign, hours and minutes out of it; a bare GMT is zero. A second rule turns the minutes back into a label: zero reads UTC, and anything else reads UTC with a sign and the hours, adding the minutes only when they are not zero. At the January instant London reads UTC, New Delhi reads UTC+5:30 and Kathmandu reads UTC+5:45; the minutes are part of the answer.

A comparison rule exported beside the formatters writes the difference between a city’s offset and the viewer’s as a sentence: an equal offset reads “Same time as you”, anything else the hours and minutes ahead of or behind you. With the viewer’s zone fixed to London’s, at the same instant it writes:

City	Against London
New York	5 hours behind you
Los Angeles	8 hours behind you
London	Same time as you
Tokyo	9 hours ahead of you
Sydney	11 hours ahead of you
Singapore	8 hours ahead of you
New Delhi	5 hours 30 min ahead of you
Kathmandu	5 hours 45 min ahead of you

January against July

Change only the instant and the offsets can change. The second fixed instant is 09:00:00 UTC on Tuesday, July 14, 2026; both instants are 9:00 AM in UTC. Between them the offsets of New York, Los Angeles, London and Sydney moved, and not all in the same direction; those of Tokyo and Singapore did not. The reading moves with the offset — New York shows 4:00 AM at the first instant and 5:00 AM at the second — and so does the short zone label the formatter supplies, from EST to EDT.

City	January	July	Moved
New York	`UTC−5`	`UTC−4`	yes
Los Angeles	`UTC−8`	`UTC−7`	yes
London	`UTC`	`UTC+1`	yes
Tokyo	`UTC+9`	`UTC+9`	no
Sydney	`UTC+11`	`UTC+10`	yes
Singapore	`UTC+8`	`UTC+8`	no

The page states no rule for which zones move or when: it asks the time-zone data shipped with your browser for the offset at the instant shown, and that is the whole of its daylight-saving handling. The time zone converter applies the same lookup to a date you type.

The hands on the dial

The analog face is drawn from the same instant. The engine’s hand rule reads the hour, minute and second for the zone from a 24-hour formatter, then places the hour hand at (hour mod 12 + minute ÷ 60 + second ÷ 3600) × 30 degrees, the minute hand at (minute + second ÷ 60) × 6 and the second hand at second × 6, clockwise from twelve, so the hour hand creeps rather than jumps. A third fixed instant, 09:41:30 UTC on Wednesday, January 14, 2026, for three cities:

City	Reading	Hour hand	Minute hand	Second hand
London	`09:41:30`	290.75°	249°	180°
New Delhi	`15:11:30`	95.75°	69°	180°
Kathmandu	`15:26:30`	103.25°	159°	180°

The second hand sits at the same angle on all 3 faces, because the readings differ only in hours and minutes, and the minute hands do not agree, because 2 of the 3 offsets are not whole hours.

The default set, and the finder

A first visit shows 6 cities: New York, Los Angeles, London, Tokyo, Sydney and Singapore. They come from a curated list of 63 entries, each tied to an IANA zone identifier. The engine’s naming rule turns an identifier back into a place: one in the list gives the city and country, so Asia/Kolkata gives New Delhi, India; one outside it gives its last segment with underscores replaced by spaces, so America/Port_of_Spain gives Port of Spain.

The search field and the Browse-by-region panel reach a larger place index — the footer credits GeoNames for the place data — and each result shows its zone identifier and its offset at the current instant, formatted by the same rule as the cards. Any card can be moved into the hero.

The tools

The strip under the grid leads to the 8 tools; each has a page of its own that explains it in the same terms.

Countdown — counts a duration, or down to a date and time read in your own zone, from one stored end instant.
Pomodoro timer — a fixed focus interval, a short break after each and a longer one after a set number, each phase chained from the last one’s end.
Interval timer — compiles prepare, work, rest and cool-down into one plan with cumulative offsets, so your position is one subtraction.
Speech timer — a band — On time, Wrap up, Final minute or Over time — chosen purely from the time remaining, with a text label as well as a colour.
Stopwatch — elapsed time against a monotonic browser clock, unaffected by a correction to the system clock while it runs.
Alarm — rings once at a local time; a time already passed today rolls forward to tomorrow, and the tab has to stay open.
Time zone converter — a wall-clock reading in one zone to the matching instant in another, with each offset looked up for the date typed.
Day of the week — the weekday of any date by integer arithmetic on the proleptic Gregorian calendar, independent of your zone and the device’s date object.

The guides and the methodology

The 7 guides take the timers and the calendar tool one mechanism at a time, in reading order:

The guides index lists them in the same order; the methodology page sets out how every tool keeps time.

Where the clock stops

Two inputs feed the clock: this device’s reading, checked against the site’s own time server when the status line says so, and the IANA zone data shipped with your browser, daylight saving included. How the two are combined is the subject of the section on how each city’s time is computed, above; what follows here is where they stop. The clock cannot confirm an official time: verify a flight, a filing or a market open against the authoritative source.

Nor is the clock a tool that sounds at an instant. For the tools that are, the methodology page draws one line, described rather than simulated: whenever a tick runs the display is correct for that instant, but whether a cue sounds at that instant depends on the device staying awake and the tab staying open — for every one of them. What separates the alarm from the 4 timers with a stored envelope — pomodoro, speech, interval and countdown — is what it keeps: they save their running state as epochs and resume from them after a reload, while the alarm writes nothing to storage and its readout shows the time it is set for rather than a count, so a reload brings back a page with no alarm set.

Questions

Which time zone does the large clock use?: Your device's own zone, as your browser reports it, until you move one of your city clocks into the hero. The heading on the clock names what is shown: beneath the time on the digital panel, on the face itself on the dial.
Why does a city's offset read differently in summer and winter?: Because the clock asks the time-zone data for the offset at the instant it is showing. New York reads UTC−5 at the page's fixed January instant and UTC−4 at its fixed July instant, while Tokyo reads UTC+9 at both.
Why do some offsets show minutes?: Because the zone's offset is not a whole number of hours and the label keeps the minutes: at the January instant New Delhi reads UTC+5:30 and Kathmandu reads UTC+5:45.
Are my cities saved?: Your city list, the 12/24 choice, the hero clock and the face you picked are kept in this browser's storage and are not transmitted. The clock asks the site's own time server for a timestamp to check this device's clock; that request carries no typed input. The place finder loads its place index from this site when you first search or browse.
Does the clock keep running while the tab is in the background?: Nothing runs while the tab is closed. While it is open, the page formats the current instant once a second, and on your return the next tick formats the instant then, so nothing has to catch up. The tools that sound a cue hold to the same line on their displays — correct whenever a tick runs — but whether the cue sounds depends on the device staying awake and the tab staying open, for every one of them. The alarm also keeps no stored envelope: the pomodoro, speech, interval and countdown timers resume from saved epochs after a reload, while a reload brings back the alarm page with nothing set.
How many cities can I show?: On a first visit the grid is already full: it holds as many cards as the default set fills, 6, so choosing another city asks which of your clocks it should replace, and the new card takes that clock's place.

Everything here runs in your browser: the clocks format this device's own reading for every zone on screen with the time-zone data your browser ships, your city list and display choices stay in this browser's storage, and the figures above were computed from the clock engine when the site was built. The methodology page sets out how every tool keeps time, and the guides index lists the guides.

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