International Date Line — World Map, Countries It Touches, and Why It Zigzags

The International Date Line is the imaginary line in the Pacific Ocean where each calendar day begins. Anchored on the 180° meridian, it deviates politically around Russia, the Aleutians, Kiribati, Samoa, Tokelau, and Tonga to keep each country on a single date. Cross it eastward to subtract a day; westward to add one.

What is the International Date Line? Definition and Geographic Facts

The International Date Line (IDL)is the imaginary line in the Pacific Ocean that marks the boundary between one calendar day and the next. Cross it eastward and the date moves back by one day; cross it westward and the date moves forward by one day. It is the operational complement of the Prime Meridian at Greenwich: the meridian sets where Earth's longitude reference is, and the IDL determines where the day rolls over.

The IDL is anchored on the 180° meridian — the antimeridian directly opposite Greenwich on the other side of Earth. Geographically, the 180° meridian is a precise line of longitude, 20,037 km long, running pole to pole. Politically, the IDL deviates from 180° wherever it would otherwise split a country into two date zones. The deviations are individual sovereign decisions, not a treaty — there is no international body that maintains the IDL.

Where is the International Date Line on a world map?On any standard Pacific-centred world map, the IDL is the wavy vertical line running through the central Pacific Ocean. It descends from the North Pole through the Bering Strait (deviating west around Russia and east around the western Aleutians), then runs south through the open Pacific (deviating far east around Kiribati's Line Islands and far west around Samoa, Tonga, and the eastern edge of New Zealand's waters), before terminating at the South Pole through Antarctica.

Almost the entire IDL is over open ocean. The 180° meridian touches only three pieces of land: Wrangel Island (Russia), the western Aleutian Islands (USA), and Taveuni plus parts of Vanua Levu (Fiji). All other countries on either side of the IDL — Kiribati, Samoa, Tonga, Tokelau, New Zealand, the Cook Islands, French Polynesia — are reached only by deviation, not by the geographic line.

How to use this International Date Line map

1. Open the world map. The vertical purple line is the 180° meridian — the geographic anchor of the International Date Line. The IDL itself is not a strict 180° line; it deviates politically around several countries to keep each on a single calendar date. Three countries with land directly on 180° are highlighted: Russia (Wrangel Island), the United States (western Aleutians), and Fiji (Taveuni).
2. Compare the geographic 180° line with the political IDL. The map shows the 180° meridian. The actual IDL deviates eastward around Russia and the Aleutians (so they share dates with the rest of their countries) and far eastward around Kiribati's Line Islands (so the entire republic is on one date). Below the map, the country detail explains each deviation.
3. Click any highlighted country to see latitudes and length traversed. Click any highlighted country (or a row in the table) to see entry/exit latitudes where the 180° meridian crosses the country's territory. The intersections are tiny — Wrangel Island and the Aleutians together account for under 50 km of land along the line; Fiji's main encounter is on Taveuni island.
4. Read the date-arithmetic notes. Below the map: how crossing the IDL works (eastward subtracts a day, westward adds one), the famous 21-hour gap between Big Diomede (Russia) and Little Diomede (USA) only 4 km apart, Kiribati's 1995 eastward jump, Samoa's 2011 westward jump, and why the date line isn't legally binding worldwide.

The 180° meridian vs. the political IDL

Two related but distinct lines run through the Pacific:

• The 180° meridianis a fixed geographic line, exactly 180° of longitude away from Greenwich. It is set by Earth's geometry and is permanent. The map at the top of this page shows the 180° meridian.
• The political International Date Line is an informal convention that follows 180° most of the way but zigzags wherever it would split a country. It is drawn on every IDL map you see — typically as a wavy line that bulges east around Kiribati and west around Samoa.

The two lines coincide for most of their length over open Pacific Ocean. They diverge in five places: the Bering Strait (the IDL bulges west of Russian territory), the western Aleutians (the IDL bulges east of US territory), Kiribati's Line Islands (the IDL bulges far east, putting the islands on UTC+14), and Samoa, Tokelau, and Tonga (the IDL bulges west, putting them on UTC+13 or UTC+14 alongside New Zealand).

Six countries touched by the date line (and the deviations they cause)

Three countries have land directly on the 180° meridian — Russia, USA, Fiji. Three more force major political deviations of the IDL — Kiribati, Samoa, and Tonga. Below is what each country contributes to the line's shape.

How crossing the date line works

Crossing the IDL changes the calendar date by exactly one day; the time on the clock does not change at the moment of crossing because the time zones on either side are 24 hours apart in the calendar but differ by zero on the clock.

• Eastward (Asia → Americas): the date moves back by one. A 10-hour flight from Tokyo (UTC+9) to Honolulu (UTC-10) leaving Tuesday 9:00 lands Tuesday 7:00 on the same day — you arrive before you left, calendar-wise.
• Westward (Americas → Asia): the date moves forward by one. A 10-hour flight from Honolulu (UTC-10) to Tokyo (UTC+9) leaving Tuesday 9:00 lands Wednesday 14:00 — Tuesday is partially skipped.
• Across both lines: a westbound around-the-world flight crosses the IDL once and the date moves forward exactly once during the trip; an eastbound flight crosses the IDL once and the date moves back. Either way, your wristwatch and calendar end up correct when you return home.

The IDL only changes the date — not the time. Time-zone offsets handle the clock; the IDL handles the day. They work together: as you fly westward across the world, you gradually lose hours via time zones, but you gain a full day at the IDL, balancing the books.

The Diomede Islands: 4 km apart, 21 hours different

The most extreme example of the date line on land is the Diomede Islands in the Bering Strait. Big Diomede (Ratmanov Island) is Russian; Little Diomede is American. The two islands are only 3.8 km apart, separated by the United States–Russia maritime border which follows the IDL.

Big Diomede is on Anadyr time (UTC+12); Little Diomede is on Alaska time (UTC-9). On the clock the difference is 21 hours, but in calendar terms — accounting for the IDL — Big Diomede is roughly “a day ahead” of Little Diomede. From Little Diomede on a clear morning, you can see Big Diomede across the strait — looking literally one day into the future. The islands are sometimes nicknamed “Yesterday Island” (Little Diomede, USA) and “Tomorrow Island” (Big Diomede, Russia).

Kiribati's 1995 jump: the easternmost time zone on Earth

On 1 January 1995, the Republic of Kiribati moved the International Date Line eastward to encompass its entire territory. Before the change, Kiribati was split: the Gilbert Islands (with the capital, Tarawa) used UTC+12, while the Line Islands far to the east used UTC-10 — a calendar gap of one full day across the same country.

The Line Islands shifted from UTC-10 to UTC+14, the new easternmost time zone on Earth. Kiritimati (Christmas Island) — the largest atoll in the Line group — became the first inhabited place to see each new day, a status it shares with the rest of Kiribati. The practical effect for Christmas Island residents: the local clock reads the same as before, but the calendar date moved forward by one. The same time of day is now Tuesday instead of Monday.

The 1995 change was made by presidential proclamation, not by international treaty. It is a textbook example of how the IDL is a sovereign political choice. No other country recognised or contested the change — it simply became the new convention.

Samoa and Tokelau's 2011 leap: the day that didn't exist

On 30 December 2011, the Independent State of Samoa and the New Zealand territory of Tokelau crossed the International Date Line westward. The change moved Samoa from UTC-11 to UTC+13. Friday 30 December 2011 was skipped entirely — the date does not exist in Samoan civil records. Citizens went to bed on Thursday 29 December and woke up on Saturday 31 December.

The reason was economic. By the early 2010s, Samoa's primary trading partners were New Zealand, Australia, and China — all on the western side of the IDL. Operating a day behind cost businesses two working days each week (Saturday in Samoa was Friday in Auckland; Sunday in Samoa was Monday in Auckland). After the change, Samoa is 24 hours ahead of American Samoa, only 100 km away — the largest date-line gap between two neighbouring populated places on Earth.

Why isn't the date line straight?

The 180° meridian was chosen as the natural anchor for the IDL because it is exactly opposite Greenwich and runs almost entirely through ocean. But three forces have progressively bent the date line away from a strict 180°:

• National unity:countries don't want internal date splits. Russia keeps Wrangel and the Bering coast on Moscow-aligned time; the US keeps the western Aleutians on Alaska time; Kiribati merged its split halves in 1995.
• Trade alignment:Pacific island nations (Samoa, Tokelau, Tonga, Kiribati's capital) align with their largest trading partners. New Zealand and Australia anchor the western Pacific cluster; the US/American Samoa anchor the eastern.
• Sheer convenience: the IDL is a convention, not a treaty. Countries adjust it at will. There is no enforcement mechanism and no international body that would object.

The IDL in Antarctica

South of about 60° S, the IDL becomes meaningless. Antarctic research stations choose whatever time zone is most convenient — usually that of their home country or their logistical hub. McMurdo Station (US) uses New Zealand time (UTC+12 or UTC+13 in summer); Vostok Station (Russia) uses UTC+6; the South Pole's Amundsen-Scott Station uses New Zealand time because all flights in originate from Christchurch. Near the South Pole, every meridian — including 180° — converges to a single point, and the very concept of a line of longitude collapses.

Related tools and resources

For the meridian on the other side of Earth — where 0° longitude was set in 1884 — see our Prime Meridian tool. For the major parallels of latitude, see the Equator, Tropic of Cancer, Tropic of Capricorn, Arctic Circle, and Antarctic Circle.

For other coordinate-related tools: find your antipode on the opposite side of Earth (every point's antipode is on the antimeridian), find your latitude and longitude, or check the time difference between two locations — a useful way to see how the IDL affects east-west travel.

Frequently asked questions about the International Date Line