This guide covers What Is the International Date Line? | 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a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.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 imaginary line in the Pacific Ocean where the calendar date changes. It runs roughly along 180 degrees longitude, opposite the Prime Meridian at Greenwich, and it is the reason that when it is Monday in Tokyo it can still be Sunday in Hawaii.

Crossing the line changes the date by one day. Travelling west across it — from the Americas towards Asia — you move the calendar forward a day: Sunday becomes Monday. Travelling east — from Asia towards the Americas — you move it back: Monday becomes Sunday. The time of day does not change, only the date.

The line is not straight. It bends around island nations so that no country is split between two dates: it goes around Kiribati, Fiji, Tonga and Samoa, and around Alaska's Aleutian Islands. In 2011 Samoa moved the line itself, skipping Friday 30 December 2011 entirely, so that the country would share its working week with Australia and New Zealand rather than the United States.

The date line is a convention, not a law of nature — there is no international treaty that defines it. But every country respects it, because without it, world travel and world trade would have no agreed calendar. It is the counterpart of the Prime Meridian: Greenwich divides the world in space, the date line divides it in time.

In practice

The date line exists because the Earth is round and the day has to start somewhere. If you travel west around the world, 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, or you would arrive home a day ahead of the calendar. The International Date Line is that line, running through the Pacific at roughly 180 degrees longitude.

It is not straight, and it is not fixed. It bends around Kiribati, Tonga and Samoa so that whole countries stay on one side, and it has been moved by governments — most famously by Samoa in 2011, which skipped 30 December entirely to move to the west side. The line is a human invention, drawn for convenience, and it can be redrawn.

The line is also the reason the new day starts in the Pacific. The first places on Earth to see each new day are Kiribati's Line Islands, on UTC+14:00, and the last are Baker Island and Howland Island, on UTC−12:00, which are uninhabited. The span between them is 26 hours, which is why two people can be living in different calendar days at the same moment — and why a meeting scheduled for 'Monday' needs a time zone attached.

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

Where is the International Date Line?

It runs through the Pacific Ocean, roughly along 180 degrees longitude, opposite the Prime Meridian at Greenwich.

What happens when you cross it?

The date changes by one day. Crossing westward you gain a day; crossing eastward you lose one. The time of day does not change — only the date.

Why is the line not straight?

It bends around Kiribati, Tonga and Samoa so that no country is split across two dates. Kiribati's Line Islands are on UTC+14:00, the earliest time on Earth.

Can a country move the date line?

Yes — it is a convention, not a law of nature. Samoa moved it in 2011, skipping Friday 30 December 2011 entirely, to align its working week with Australia and New Zealand.

What is the time difference across the date line?

Up to 26 hours: from UTC+14:00 on one side to UTC−12:00 on the other. Two people can be living in different calendar days at the same moment.

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.