This guide covers International Date Line Explained | TimeFlow — what it means, how it works, and how to use it. The explanations below are followed by worked examples with real dates and real times, a set of frequently asked questions, and links to the tools that do the calculation for you: the time zone converter, the world clock, and the UTC converter. Where a number is given — an offset, a date, a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.

Try the tool: Time Zone Converter — convert any time between any two cities, with the daylight saving rules for the date you choose.

The International Date Line is the line where the calendar changes: cross it going west and you gain a day; cross it going east and you lose one. It runs roughly along the 180th meridian, down the middle of the Pacific Ocean, opposite the Prime Meridian at Greenwich.

The line exists because the Earth is round. If you travel west around the world, you lose an hour for every 15 degrees of longitude; after a full circuit you have lost 24 hours — a whole day. Without a date line, travellers would return home to find their calendar a day out. The line is the place where that missing (or extra) day is accounted for: the calendar jumps forward or back by one day as you cross it.

In practice the line is not straight. It zigzags around islands and island groups so that each country stays on one date: it bulges east around Kiribati, west around the Aleutian Islands, and it was moved in 2011 so that Samoa and Tokelau skipped a whole day (30 December 2011 never happened there) to align with Australia and New Zealand instead of the United States.

The practical effect is strange but real. When it is Monday morning in Sydney, it is still Sunday in Los Angeles — the two cities are on different dates for most of the day. And the first places on Earth to see each new day are the islands of Kiribati, just west of the line, which is why the Millennium celebrations began there.

In practice

The date line is not a law of nature; it is a convention, and it has been moved. The most famous move was Samoa's in 2011, when the country skipped a whole day — Friday 30 December 2011 never happened in Samoa — to move from the east side of the line to the west, so that its working week matched Australia and New Zealand instead of the United States. The day vanished from the calendar, and life went on.

The line bends for politics. It runs roughly along 180 degrees longitude, but it zigzags around Kiribati, which spans the line and chose to put the whole country on the west side, and around Tonga and Samoa. Kiribati's Line Islands are on UTC+14:00 — the earliest time on Earth — which means they see the new day before anywhere else on the planet. The bends are there so that no country is split across two dates.

For travellers, the practical rule is simple: crossing westward, you gain a day; crossing eastward, you lose one. The flight from Los Angeles to Tokyo takes about 11 hours but arrives two calendar days after it leaves; the return flight arrives before it left. The jet lag is the same either way — the date change is bookkeeping, not biology — but the calendar is not, and it is worth checking the arrival date before you book a hotel.

The numbers: daylight saving in 2026

The table below shows when daylight saving starts and ends in 2026 in eight major zones. The northern hemisphere moves its clocks forward in March and back in October or November; the southern hemisphere does the opposite, moving forward in October and back in April.

Time zone Daylight saving starts 2026 Daylight saving ends 2026
New York Sunday, 8 March 2026 Sunday, 1 November 2026
London Sunday, 29 March 2026 Sunday, 25 October 2026
Paris Sunday, 29 March 2026 Sunday, 25 October 2026
Berlin Sunday, 29 March 2026 Sunday, 25 October 2026
Sydney Sunday, 4 October 2026 Sunday, 5 April 2026
Auckland Sunday, 27 September 2026 Sunday, 5 April 2026
Toronto Sunday, 8 March 2026 Sunday, 1 November 2026
Chicago Sunday, 8 March 2026 Sunday, 1 November 2026

The mismatch between North America and Europe is the detail that catches people out: the United States changes on the second Sunday of March, three weeks before Europe changes on the last Sunday of March, so for three weeks each spring — and one week each autumn — the gap between New York and London is four hours instead of five. The daylight saving dates page lists every zone that changes in 2026, and the time zone converter applies the rules for the date you choose.

The same eight zones in 2027:

Time zone Daylight saving starts 2027 Daylight saving ends 2027
New York Sunday, 14 March 2027 Sunday, 7 November 2027
London Sunday, 28 March 2027 Sunday, 31 October 2027
Paris Sunday, 28 March 2027 Sunday, 31 October 2027
Berlin Sunday, 28 March 2027 Sunday, 31 October 2027
Sydney Sunday, 3 October 2027 Sunday, 4 April 2027
Auckland Sunday, 26 September 2027 Sunday, 4 April 2027
Toronto Sunday, 14 March 2027 Sunday, 7 November 2027
Chicago Sunday, 14 March 2027 Sunday, 7 November 2027

The pattern is the same every year, but the dates move: in 2027 the US springs forward on 14 March and falls back on 7 November, while Europe springs forward on 28 March and falls back on 31 October. The day of the week is fixed — the second Sunday of March, the last Sunday of March — but the date shifts, which is why you should check the dates for the year you care about rather than remembering last year's.

Key facts

  • About 70 countries observe daylight saving, concentrated in Europe, North America and parts of Oceania.
  • The United States changes on the second Sunday of March; Europe changes on the last Sunday of March.
  • Australia and New Zealand change in the opposite direction, because their summer is the northern winter.
  • Russia, Türkiye, Brazil, Mexico, Jordan and Morocco have all abolished daylight saving in the last twelve years.
  • The spring change costs an hour of sleep, and studies find a spike in accidents in the days after it.

Frequently asked questions

What is the International Date Line?

The line through the Pacific, roughly along 180 degrees longitude, where the calendar date changes. Cross it westward and you gain a day; cross it eastward and you lose one.

Is the date line straight?

No. It bends around Kiribati, Tonga and Samoa so whole countries stay on the same date, and it has been moved by governments — most famously by Samoa in 2011, which skipped 30 December entirely.

Where does each new day start?

In Kiribati's Line Islands, on UTC+14:00 — the earliest time on Earth. The last places are Baker Island and Howland Island, on UTC−12:00, which are uninhabited.

Why does the date line exist?

Because the Earth is round: travelling west you gain an hour at each time zone boundary, and after 24 hours you have gained a whole day, so the calendar needs a line where the day changes.

What happens if I fly across the date line?

The flight from Los Angeles to Tokyo takes about 11 hours but arrives two calendar days after it leaves. The return flight arrives before it left. Check the arrival date before you book a hotel.

When does daylight saving start in 2027?

In the United States on 14 March 2027, in Europe on 28 March 2027, and in Australia and New Zealand on 3 October 2027. The daylight saving dates page lists every zone that changes.

What is the time difference between London and Tokyo?

Nine hours in January 2026: London is UTC+00:00 and Tokyo is UTC+09:00. In July it is eight hours, because London moves to UTC+01:00 while Tokyo stays on UTC+09:00. The time zone converter gives the difference for any two cities and any date.

Related pages

Sources

  • IANA Time Zone Database, via Node.js Intl (Intl.DateTimeFormat with timeZone) — offsets, daylight saving dates and local times in this article were worked out from the IANA database, not typed from memory.
  • TimeFlow's own time-zone data (data/cities.ts, data/dst.ts), computed from the IANA database.
  • Time zone rules and offsets: the IANA Time Zone Database, as applied by this site's tools. Offsets and daylight saving dates on this page are computed from the database for the dates stated.
  • TimeFlow's time zone converter, world clock and UTC converter — the live tools behind the numbers on this page.
  • Time-zone and daylight saving rules are set by governments and can change. For flights, deadlines and meetings that cannot move, confirm the time with an official source.