World Clock: Live Time in 418 Cities at a Glance

By Kugel · Sydney, Australia

A world clock shows the current local time in several places at once, so that you can compare them without doing subtraction in your head. The clock on this page opens with six cities placed side by side, every card reading from the same instant, and you can reshape that list around the places that matter to you.

The set behind the tool holds 418 time zones taken from the IANA database that ships with every modern browser. Any of them can be added to the board, any of them can be removed, and the list you build is stored on your own device, so the same cities are waiting when you come back.

What follows explains what each card reports, how a UTC offset is read, why two cities sit five hours apart for most of the year and four hours apart for three weeks in spring, and how to turn the board into a scheduling instrument rather than a curiosity.

What Each Card Tells You

Every city on the board gets a card, and the card carries six pieces of information at once. The country flag and the city name identify the place. Below them the local time runs in a 12-hour format with hours, minutes, and seconds, and the seconds move every second, because the whole board is refreshed on a one-second interval from a single shared instant.

The weekday and the calendar date sit under the time, and they are not decoration. For a city far enough to the east or west, the date at that location can differ from yours by a full day, which is exactly the kind of detail that ruins a hand-built schedule. Next to the date you see either a sun or a moon: the sun means the local hour falls between six in the morning and eight in the evening, and the moon covers the rest of the clock.

Two badges sit at the bottom of each card. The first is the UTC offset of the zone right now, written the way modern browsers write it, for example UTC+5:30 or UTC-4. The second is the difference between that offset and the offset your own device is running on, so a reading of "+2h" means the city is two hours ahead of you at this moment. When a zone is a half hour or three quarters of an hour away, the badge shows the minutes as well, as in "-3h 30m".

The third badge answers a practical question rather than a factual one. It reports whether the local hour falls inside a standard working window, taken here as eight in the morning to six in the evening, or outside it. A card marked "Off hours" is a city where nobody is likely to answer the phone.

How to Build Your City List

The board starts with London, San Francisco, Cairo, Las Vegas, Chicago, and Tokyo, six zones spread across the globe so that the tool is useful before you have changed anything. From there the controls sit in a single row above the cards.

The dropdown on the left is the way in. It lists every zone the tool knows, each row showing a flag and a city name. Selecting one appends a card for that location and clears the selector, ready for the next pick. The list is filtered as you go: zones already on the board disappear from the dropdown, so the same city cannot be added twice, and if a zone does somehow repeat, the tool reports that the city is already displayed instead of drawing a duplicate.

Each card carries two buttons in its top right corner. The cross removes that city from the board. The copy button writes a one-line summary of the card to your clipboard, in the form "City: 14:32:07 PM (UTC+2) — Wed, Sep 23", which is the shape you want when the reading has to go into a message or a ticket rather than stay on screen.

The button beside the dropdown reorders the board. Pressed once, it sorts the cards by UTC offset, from the westernmost zone to the easternmost, which makes a path around the globe read left to right. Pressed again, the original order returns. The counter at the end of the control row reports how many cities are currently on the board, which is useful once the list has grown past a single screen of cards.

Reading a UTC Offset

A UTC offset states how far a place's civil time stands from Coordinated Universal Time, and Coordinated Universal Time is the fixed anchor the whole system is measured against. Offsets run from UTC-12, used on Baker Island in the Pacific, to UTC+14, used by the Line Islands of Kiribati, a span of twenty-six hours. That is why two places can be on different calendar dates at the same instant.

The arithmetic is a single step in each direction. To turn a local reading into UTC, subtract the offset; to turn a UTC reading into local time, add it. Nine in the morning in Tokyo, which sits at UTC+9, is midnight UTC. Midnight UTC is 5:30 in the morning in Mumbai, because India runs half an hour off the whole-hour grid.

A time zone is not the same thing as an offset. A zone is a named rule set for a place, and the offset is whatever that rule set produces on a particular date. The IANA database, the same one that Windows, macOS, Linux, and every major browser use, tracks several hundred named zones and is revised several times a year as governments move their clocks.

Standard UTC Offsets for Major Cities

The table below gives the standard, non-summer offsets for a set of widely used cities.

Two cities can share an offset and still be different zones. Lagos at UTC+1 and Berlin at UTC+1 keep the same winter time, and they part company in summer, when Berlin moves forward and Lagos does not. Reading the offset alone tells you the time now; reading the zone tells you what the offset will do later.

Daylight Saving Time Moves the Gap

Daylight saving time shifts a region's clocks forward by an hour for part of the year and then brings them back. Only about seventy countries do it, roughly a third of the world, and the ones that do change on dates that were chosen locally rather than agreed internationally. The United States moves forward on the second Sunday of March and back on the first Sunday of November, which in 2026 means the eighth of March and the first of November. The European Union moves on the last Sunday of March and the last Sunday of October, the twenty-ninth of March and the twenty-fifth of October in 2026.

Those two calendars do not line up, and the days between them are where the trouble lives. From the eighth of March to the twenty-ninth of March in 2026, the United States is on summer time while Europe is still on winter time, so the gap between New York and London narrows from the usual five hours to four. The same thing happens in reverse at the end of October, when Europe falls back a week before the United States does. Two windows a year, a few weeks long each, in which the familiar number is wrong.

The southern hemisphere runs the whole arrangement upside down. Sydney and Auckland move forward in October and back in April, so for six months of the year an Australian city is closer to London than its longitude suggests, and a meeting planned in January and repeated in July lands at a different hour for everyone.

None of this has to be tracked by hand. Because each card is computed from the IANA rules for its own zone on the current date, the offsets on the board are correct on both sides of every transition, and the difference badge between two cities updates the moment one of them changes. A board that reads "+5h" in February will read "+4h" during the March window without anyone touching it.

The Zones That Are Not Whole Hours

The mental picture of twenty-four tidy vertical bands, an hour apart, is a teaching device rather than a description of the world. Several zones sit on a fraction of an hour, and their existence is the reason a converter that only counts whole hours produces answers that are off by thirty minutes.

India runs at UTC+5:30 all year, which puts half an hour between it and every whole-hour zone on either side. Nepal goes further and uses UTC+5:45, one of the few quarter-hour offsets in the world. Parts of Australia use half-hour zones, including Adelaide at UTC+9:30 in winter, and Newfoundland in Canada sits at UTC-3:30. The Chatham Islands, east of New Zealand, use UTC+12:45.

The practical consequence shows up whenever a city on a fractional offset is compared with a city on a whole hour. New York at UTC-4 against Mumbai at UTC+5:30 is a difference of nine and a half hours, not nine or ten, and a schedule built on whole hours quietly drifts. The difference badge on each card in this tool reports minutes when there are any to report, so the half hour is visible instead of rounded away.

Scheduling a Meeting Across Time Zones

The board is most useful when the question changes from "what time is it there" to "when can we all talk". The business-hours badge does the first pass of that work: scroll the cards, and the ones marked with working hours are the cities that can reasonably join a call, while the ones marked "Off hours" cannot without someone paying a price.

A workable overlap has to be searched for rather than assumed. Take a team spread over New York, London, and Tokyo. New York and London share a comfortable afternoon window, because five hours apart is close enough for both ends of a business day to touch. Tokyo, nine hours ahead of London and fourteen ahead of New York, shares almost nothing with either: the Tokyo working day ends around the time New York is waking up. A call that suits New York and London at four in the afternoon puts Tokyo at midnight.

The honest answers in that situation are three, and the tool makes each of them easy to see. One is to accept an early or late slot and rotate who takes it, so the same office is not always the one on a call at eleven at night. The second is to shorten the synchronous part and let the rest travel as a written update, which is the pattern most distributed teams settle into once the arithmetic becomes obvious. The third is to move the meeting to the pair of cities that can genuinely share a working hour and let the third join asynchronously.

What the clock removes is the guesswork. Instead of converting three times and second-guessing the result, you read three badges and know immediately which cities are inside their working day.

Who Uses a World Clock Every Day

Remote teams are the obvious audience, and they are the reason the business-hours badge exists. A support desk that follows the sun, a sales team with customers on three continents, and an engineering group split between two offices all need the same thing: a fast, accurate read on who is awake and working.

Travelers use it differently. Before a flight, a world clock settles what the arrival time will feel like, whether the destination is a day ahead, and how far the body clock has to travel. Traders and market watchers keep the board pinned to the financial centres they follow, because an exchange's opening bell is a local time that moves against their own twice a year.

Families and friends spread across countries use it for the simplest purpose of all, which is knowing when a call will be welcome rather than an interruption. Nobody enjoys being the one who rang at three in the morning, and a single glance at the moon icon on a card prevents it.

Where Your City List Is Kept

Everything about this tool runs inside the browser. Each reading is produced by the browser's own internationalisation engine from the zone rules it already holds, so the clock never asks a server what time it is, and the numbers on the cards cannot drift with a network delay.

The list of cities you build is saved in your browser's local storage under a single key, as a short array of zone names. It is written after the board first loads and updated every time you add or remove a city, which is why the list survives a refresh and a restart. Nothing about the list is uploaded, because there is nowhere for it to go: no account is created, no cookie identifies you, and clearing your browser data removes it completely.

That design has one consequence worth stating plainly. The board is personal to the browser it was built in, so a list assembled on a laptop does not appear on a phone unless you add the same cities there. The trade is deliberate: convenience of recall in exchange for the passing of any data to a server.

Kugel

Sydney, Australia · SO reputation 19992 · Badges: 16🥇76🥈106🥉 · SO member since 2009