International Date Line Explained

2026-02-04 · 8 min read

The International Date Line is an imaginary boundary that runs mostly near 180° longitude in the Pacific. It separates two consecutive calendar dates.

How It Works

• Crossing westward adds one day.
• Crossing eastward subtracts one day.

Two nearby islands can therefore show different calendar dates at the same moment.

Why the Line Zigzags

The line is not straight because it bends around national borders and island groups. It zigzags near Kiribati, Samoa, Tonga, and Fiji so territories can keep a consistent local date.

Key Modern Changes

Kiribati moved the Line Islands in 1995 so the whole country could share one date. Samoa switched sides in 2011 and skipped Friday, December 30, 2011, to align its workweek with Australia and New Zealand.

Historical Background

The 1884 International Meridian Conference established Greenwich as the prime meridian framework; the date line developed as the practical counterpart on the opposite side of the globe.

Practical Effect Today

Kiribati’s Line Islands use UTC+14, the farthest-ahead civil time in the world.

See global offsets on the timezone map.