UTC (Coordinated Universal Time)
utc
The primary time standard by which the world regulates clocks and time, serving as the basis for civil timekeeping globally.
GPS Time
gps time
Overview
GPS Time (GPST) is the internal time scale of the Global Positioning System. It began at 00:00:00 UTC on January 6, 1980 and runs continuously without leap-second adjustments. As of 2026, GPST is 18 seconds ahead of UTC because UTC has inserted 18 leap seconds since 1980.
Why No Leap Seconds
GPS positioning relies on measuring signal travel-time differences at nanosecond precision. Inserting a leap second would introduce a discontinuity in the time scale, disrupting real-time navigation calculations. By excluding leap seconds, GPST guarantees unbroken continuity. GPS receivers convert GPST to UTC using the UTC offset value broadcast in the navigation message.
Relationship to TAI
GPST has a fixed offset from International Atomic Time: GPST = TAI minus 19 seconds. The 19-second difference originates from the TAI-UTC gap at the time GPS operations began in 1980. Because both GPST and TAI are continuous scales without leap seconds, this 19-second offset remains constant indefinitely. After the planned abolition of leap seconds in 2035, the GPST-UTC difference will also become permanently fixed.
Was this article helpful?
Related Terms
Atomic Clock
atomic clock
An atomic clock measures time by using the quantum-mechanical transition frequency of atoms as its reference, achieving accuracies on the order of one second in hundreds of millions of years and forming the backbone of modern timekeeping.
Leap Second
leap-second
A one-second adjustment applied to UTC to keep it aligned with the Earth's irregular rotation.
Related Articles
The GPS Time System - How Satellites Use Precise Time to Find You
GPS positioning depends on precise time more than people realize. This article covers the satellite atomic clocks, the relativistic corrections that keep position errors small, the relationship between GPS time and UTC, and the week number rollover problem looming over older receivers.
Space, Time, and Relativity - How Gravity and Speed Bend the Clock
Einstein's theories of relativity show that time is not absolute. This article explains time dilation due to speed and gravity through concrete examples: GPS corrections, the twin paradox, the Tokyo Skytree experiment, and the extreme slowdowns near black holes.
How Time Zones Work - Understanding UTC Offsets and the Global Time System
Learn how time zones divide the world into regions with different local times, how UTC offsets work, and why some zones use half-hour increments.