Reading a city card
Every card on the board carries five readings. Here is what each one means, using Sydney seen from London in late October as the case.
- Big time
- Wall clock time in the city right now, ticking each second.
- Day tag
TomorroworYesterdayappears when the city sits on a different calendar date from you. Sydney spends most of a London evening on the next day.- Gap
- Hours between the city and your clock.
+11hmeans Sydney reads eleven hours later than London. - Offset
- Distance from UTC today, such as
UTC+11:00for Sydney in October. - Next change
- The next daylight saving shift the browser knows about for the zone, with its direction. Zones with no DST say so.
The weeks when the usual gap is wrong
Most people learn one number per city pair. New York is five hours behind London. That number holds for most of the year, then breaks for a week or two, because each region moves its clocks on its own schedule. Pairs across the equator move twice as often.
- The US and Canada switch on the second Sunday of March and the first Sunday of November.
- The EU and UK switch on the last Sunday of March and the last Sunday of October.
- New South Wales, Victoria, plus the ACT switch on the first Sunday of April and the first Sunday of October. Queensland does not switch.
Here is how the London gaps move over the next year, taken from the same zone database your browser uses.
| Dates | New York to London | London to Sydney |
|---|---|---|
| 25 Oct to 1 Nov 2026 | 4 h | 11 h |
| 1 Nov 2026 to 14 Mar 2027 | 5 h | 11 h |
| 14 Mar to 28 Mar 2027 | 4 h | 11 h |
| 28 Mar to 4 Apr 2027 | 5 h | 10 h |
| 4 Apr to 3 Oct 2027 | 5 h | 9 h |
| 3 Oct to 31 Oct 2027 | 5 h | 10 h |
A weekly 15:00 London call with a New York team lands at 10:00 for them most of the year, and at 11:00 during the bold weeks. Calendar apps handle this when the invite is pinned to a zone. Recurring invites typed as "10 am Eastern" in a message body do not.
Zone names beat three-letter codes
The board stores zones by their database name, such as America/Chicago, rather than by abbreviation. Abbreviations collide.
| Code | Meaning | Offset |
|---|---|---|
CST | Central Standard Time, US | UTC−06:00 |
| China Standard Time | UTC+08:00 | |
| Cuba Standard Time | UTC−05:00 | |
IST | India Standard Time | UTC+05:30 |
| Israel Standard Time | UTC+02:00 | |
| Irish Standard Time (summer) | UTC+01:00 |
A database name also carries history. America/Phoenix stays on UTC−07:00 all year because most of Arizona skips daylight saving, while America/Denver shares the winter offset then moves an hour in March. Both read "Mountain Time" on a calendar invite.
Country borders do not settle the question either. China runs one official clock, UTC+08:00, across five geographic zones. In Xinjiang, plenty of residents keep an unofficial local time two hours behind Beijing, listed in the database as Asia/Urumqi. Add whichever one the person you are calling uses.
When the calendar date flips
The date line makes the far ends of the board awkward. In January, a Friday 16:00 deadline in San Francisco falls at 13:00 on Saturday in Auckland. Teams split across the Pacific share four full working days a week, not five, since Monday morning in New Zealand is still Sunday around noon in California.
Samoa felt this hard enough to move. In December 2011 the country jumped from the east side of the date line to the west to line up its week with Australia plus New Zealand, its main trading partners. Friday 30 December 2011 never happened there. The board's weekend shading shows the same effect: watch the right edge of the Auckland row on a Friday.
Where this board falls short
- One set of working hours for every row. The strip applies your 09:00 to 17:00 choice to every city. A Madrid office with a long lunch, or a Riyadh office on a Sunday to Thursday week, needs a manual check.
- Weekends only, no holidays. Saturday plus Sunday are shaded. Public holidays, Ramadan hours, or Golden Week closures are not.
- Your device sets the time. Every clock derives from your system clock. If your laptop drifts by a minute, every city drifts with it.
- Rules come from your browser. A country changing its DST rules shows up only after your browser ships an updated zone database. The next-change scan looks thirteen months ahead.
- The board lives in this browser. Cities save to local storage on this device. A different browser or a private window starts from the default list. The cap is twelve clocks.
Comparing two zones at a future date with no live board? The timezone converter handles a single conversion faster.