UTC to GPS week and seconds
The week, seconds of week, 10-bit week and rollover era, and the GPS − and − UTC offsets for a UTC time.
A published result changed on 2026-09-23: Promoting this tool to stable removed EXPERIMENTAL_TOOL from its warnings, which moved LEAP_SECOND_TABLE_EXPIRED from index 1 to index 0 and broke v007, which pinned the index. Nothing computed changed. v007 is superseded by v025, which names the warning by its code with the meta.warnings.*.code form the runner supports, so no warning sorting above it can shift it again -- the same fix units.fuel.convert v001 took. Changelog
IERS Bulletin C (leap seconds) Bulletin C 72 runs out on 2027-06-30. Sources
It is GPS week 2436, second 432018.
- Seconds of week
- 10-bit week
- Rollover era
- GPS − UTC
- TAI − UTC
- GPS time
Provenance
- Computed by
- time.scale.gps-week 1.0.0, core 0.1.0
- Model
- GPS time = UTC + (TAI − UTC) − 19 s; week = ⌊GPS seconds since 1980-01-06 / 604,800⌋
- Accuracy
- Exact for dates the leap-second table covers
- Reference data
- version IERS Bulletin C 72 (2026-07-06) of a reference dataset
- Notes
- None
- Cites
- U.S. Space Force, Space Systems Command, IS-GPS-200N, NAVSTAR GPS Space Segment/Navigation User Segment Interfaces; International Earth Rotation and Reference Systems Service, IERS Bulletin C 72
Something look off?
How we got thisFormula, worked example, sources, and proof
Model: GPS time = UTC + (TAI − UTC) − 19 s; week = ⌊GPS seconds since 1980-01-06 / 604,800⌋
Accuracy: Exact for dates the leap-second table covers
When to use this: Use this to place a UTC time on the GPS time scale: the week and seconds of week a RINEX header, an almanac or a receiver log wants, the 10-bit week a legacy navigation message carries, and the GPS − UTC and TAI − UTC offsets in force at that instant.
Limitations: GPS − UTC depends on a published leap-second table, not a formula, so an instant past the embedded table's expiry could move by a second if the IERS announces one; the result says so with a LEAP_SECOND_TABLE_EXPIRED warning rather than leaving you to check. The 10-bit week repeats every 19.6 years, so a raw week number from a receiver means nothing without its era -- which is why the era is reported here rather than assumed. And this is GPS time, not GLONASS, Galileo or BeiDou: those have their own epochs and their own relationship to UTC.
Worked example: 2026-09-18 at 00:00 UTC. Source: add-practitioner-essentials scenario: week 2436, seconds of week 432018, GPS − UTC 18 s. It is golden test vector v001, and every build checks the tool still gives its answer within its tolerance.
You enter
- UTC time
- 2026-09-18T00:00:00Z
You get
- GPS week
- 2436
- Seconds of week
- 432018
- 10-bit week
- 388
- Rollover era
- 2
- GPS − UTC
- 18 s
- TAI − UTC
- 37 s
- GPS time
- 2026-09-18T00:00:18 GPST
Review: Not yet independently reviewed by a geodesist.
Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.
Status: version 1.0.0, core 0.1.0. See this tool in the verification report.
Changes
- 2026-09-23, result change: Promoting this tool to stable removed EXPERIMENTAL_TOOL from its warnings, which moved LEAP_SECOND_TABLE_EXPIRED from index 1 to index 0 and broke v007, which pinned the index. Nothing computed changed. v007 is superseded by v025, which names the warning by its code with the meta.warnings.*.code form the runner supports, so no warning sorting above it can shift it again -- the same fix units.fuel.convert v001 took. Changelog
Checked against: 24 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.
Sources
- IS-GPS-200N, NAVSTAR GPS Space Segment/Navigation User Segment Interfaces, U.S. Space Force, Space Systems Command, Revision N. Sections 3.3.4 (GPS time, epoch 1980 January 6) and 20.3.3.3.1.1 (10-bit transmission week number). Read free.
- IERS Bulletin C 72, International Earth Rotation and Reference Systems Service, Paris, 6 July 2026. UTC − TAI = −37 s from 2017 January 1 until further notice; no leap second at the end of December 2026. Read free.
Terms
- GPS: Global Positioning System
- The US satellite navigation system. Its time scale runs a fixed number of seconds ahead of UTC (18 s since 2017) because it never adds leap seconds. Source: IS-GPS-200 GPS interface specification
- TAI: International Atomic Time
- The continuous atomic time scale. UTC has been TAI minus 37 seconds since 2017. Source: IERS Bulletin C (leap seconds)
- UTC: Coordinated Universal Time
- The world's civil time standard, kept within 0.9 s of Earth's rotation by leap seconds. Aviation calls it Zulu time, written with a Z. Source: IERS Bulletin C (leap seconds)
GPS — Global Positioning System
The US satellite navigation system. Its time scale runs a fixed number of seconds ahead of UTC (18 s since 2017) because it never adds leap seconds.
Source: IS-GPS-200 GPS interface specification
TAI — International Atomic Time
The continuous atomic time scale. UTC has been TAI minus 37 seconds since 2017.
Source: IERS Bulletin C (leap seconds)
UTC — Coordinated Universal Time
The world's civil time standard, kept within 0.9 s of Earth's rotation by leap seconds. Aviation calls it Zulu time, written with a Z.
Source: IERS Bulletin C (leap seconds)