Where is the International Date Line?

The International Date Line runs roughly along the 180° meridian in the Pacific Ocean, from the North Pole to the South Pole. It zigzags to avoid splitting countries and island groups, notably detouring around Russia, the Aleutian Islands, and several Pacific island nations.

What happens when you cross the International Date Line?

When traveling westward across the date line, you skip forward one calendar day (e.g., from Monday to Tuesday). When traveling eastward, you go back one day (e.g., from Tuesday to Monday). The time of day stays approximately the same.

Why did Samoa change sides of the date line in 2011?

Samoa switched from the east side to the west side of the date line on December 29, 2011, skipping December 30 entirely. The change was made to align Samoa's business week with its major trading partners, Australia and New Zealand, rather than being a day behind them.

The International Date Line Explained

March 19, 2026

The International Date Line is where the calendar resets as you travel around the globe: cross it heading west and you skip forward a day, cross it heading east and you go back one. This guide explains why the line exists, why it zigzags, and how it affects travel and international business.

Why the Date Line Exists

The Earth is divided into 24 primary time zones, each about 15 degrees of longitude wide. Travel eastward all the way around the globe and you accumulate 24 hours of offset, arriving back where you started a full day ahead. The date line provides a place where the calendar resets: cross it and you add or subtract a day, canceling out the accumulated difference. Navigators understood this problem for centuries, but the 1884 International Meridian Conference formalized it by placing the prime meridian at Greenwich, making the 180-degree line on the opposite side of the globe the natural date boundary.

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The 180° Meridian and the Zigzag Path

In theory the date line should follow the 180th meridian exactly, a straight line from pole to pole. In practice it deviates significantly to avoid cutting through countries and island groups. From the north it detours east around Russia’s Chukchi Peninsula, bends west around Alaska’s Aleutian Islands, and weaves around several Pacific island nations including Kiribati (shifted eastward in 1995) and Samoa (moved to the western side in 2011). Each deviation reflects a sovereign decision about which calendar day a nation wants to be on.

Note

The International Date Line has no legal standing under international law. There is no treaty that defines its path. Each country near the 180th meridian simply chooses its own UTC offset, and the date line is inferred from those choices. This is why the line can move when a country decides to change its time zone.

Crossing the Date Line: What Actually Happens

When you cross the date line traveling westward, from the Americas toward Asia, you skip forward one calendar day. The time of day stays roughly the same; only the date changes. Cross eastward and you go back a day. This is most noticeable on trans-Pacific flights: a flight from Sydney to Los Angeles can depart in the morning and arrive the same calendar morning, or even the previous day, despite 13 hours in the air.

Example

Imagine departing Tokyo at 6:00 PM on Wednesday, heading east to Honolulu. The flight takes about seven hours. You arrive around 7:00 AM, but it is still Wednesday in Honolulu because you crossed the date line eastward and “gained” a day. You get to live Wednesday twice.

Time Zone ConverterConvert times between cities on opposite sides of the date line and see the date change reflected automatically.

Historical Changes to the Date Line

Kiribati, 1995

Kiribati straddles the 180th meridian, and before 1995 the date line split the country in two. Eastern islands were an entire day behind western ones, making it impossible for government offices to share a business day. On January 1, 1995, Kiribati shifted the line eastward so all its territory would share the same calendar day. The Line Islands, now at UTC+14, became the first places on Earth to enter each new day.

Samoa, 2011

For over a century Samoa sat on the eastern side of the date line, sharing its calendar day with the United States. As trade shifted toward Australia and New Zealand, being a day behind those partners cost Samoa an entire business day each week. On December 29, 2011, Samoa skipped December 30 entirely, moving from UTC-11 to UTC+13 and aligning its workweek with Australia and New Zealand. Neighboring Tokelau made the same switch simultaneously.

Compare times across the date line

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Tip

If you are scheduling meetings with colleagues in Pacific island nations, always verify the current UTC offset rather than relying on assumptions. Countries in this region have changed their time zones more than once, and the date line deviations can be surprising.

Interesting Edge Cases

The Diomede Islands in the Bering Strait illustrate the date line at its most dramatic. Big Diomede (Russia) and Little Diomede (United States) are only 3.8 kilometers apart, yet Big Diomede is 21 hours ahead (UTC+12 vs. UTC-9). When it is 9:00 AM Saturday on Big Diomede, it is noon Friday on Little Diomede, earning them the nicknames “Tomorrow Island” and “Yesterday Island.”

Impact on Travel and Scheduling

Airlines handle the date change automatically, so travelers mainly need to watch connecting flights: double-check that layovers are booked for the correct calendar day after crossing the line.

For businesses operating across the Pacific, the date line requires more careful attention. A deadline of “Friday” means different things depending on which side of the line you are on. A company with offices in both Tokyo and San Francisco needs to be explicit about which Friday it means. Using UTC timestamps for deadlines and deliverables eliminates this ambiguity entirely.

World ClockCheck the current time and date in Pacific cities to see the date line effect in real time.

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Frequently Asked Questions

Where is the International Date Line?: The International Date Line runs roughly along the 180° meridian in the Pacific Ocean, from the North Pole to the South Pole. It zigzags to avoid splitting countries and island groups, notably detouring around Russia, the Aleutian Islands, and several Pacific island nations.
What happens when you cross the International Date Line?: When traveling westward across the date line, you skip forward one calendar day (e.g., from Monday to Tuesday). When traveling eastward, you go back one day (e.g., from Tuesday to Monday). The time of day stays approximately the same.
Why did Samoa change sides of the date line in 2011?: Samoa switched from the east side to the west side of the date line on December 29, 2011, skipping December 30 entirely. The change was made to align Samoa's business week with its major trading partners, Australia and New Zealand, rather than being a day behind them.