International Date Line

The International Date Line (IDL) is the boundary between consecutive calendar days, extending from the North Pole to the South Pole through the Pacific Ocean. It roughly follows the 180.0° line of longitude but deviates in several places to pass around specific territories and island groups. Crossing the line eastbound reduces the date by one day, while crossing westbound adds one day. The IDL is a cartographic convention, not defined by international law, which has led to disagreements among cartographers regarding its precise course and has allowed countries through whose waters it passes to shift it for their own convenience.

The line is based on the 180° meridian, which lies halfway around the world from the historic Greenwich prime meridian. While it follows this meridian exactly in many stretches, it deviates east or west to accommodate the political and economic affiliations of affected areas. From north to south, the IDL first deviates east of Wrangel Island and the Chukchi Peninsula, then passes through the Bering Strait between the Diomede Islands. It bends west of St. Lawrence Island and St. Matthew Island, crosses between the U.S. Aleutian Islands and Russia’s Commander Islands, then returns to 180°.

All of Russia lies west of the IDL, and all of the United States lies east except for Guam, the Northern Mariana Islands, and Wake Island. The IDL stays on 180° until the equator, where it swings far east to circumscribe Kiribati, almost reaching 150°W, placing Kiribati’s eastern islands at UTC+14:00, the latest time on Earth. South of Kiribati, it returns east of 180°, passing between Samoa and American Samoa, then bends southwest back to 180° and follows it to Antarctica, though the line is conventionally not drawn onto most maps of Antarctica.