GNSS Time Converter

High-precision bidirectional conversion between GPS Time (Week & Seconds of Week), Unix timestamp, and UTC datetime. ✓ Algorithm verified (2026) – GPS epoch offset fixed + corrected historical leap second table (IERS-validated).

GPS Week / SOW → UTC / Unix
Unix Timestamp → GPS Time
Seconds since 1970-01-01 00:00:00 UTC.
Uses a validated dynamic leap‑second table (IERS data) for accurate historic GPS‑UTC offsets. For dates after 2017, the fixed 18s offset is applied.
Interpret the Unix timestamp input as milliseconds (e.g., 1733011200000). Outputs are always shown in seconds (Unix seconds).
GPS-UTC offset used: 18 seconds fixed | TAI-UTC: 37s (constant since 2017) ⓘ Details
Conversion Results

? UTC Datetime (RFC 1123): —

? ISO 8601 (UTC): —

? Unix Timestamp (s): —

? GPS Week / SOW: — , — s

⚡ GPS Epoch offset: 1980-01-06 00:00:00 UTC (315964800 Unix seconds)

Current GPS Time
GPS Epoch (Week 0, SOW 0)
Example: Week 2150, SOW 302400
Unix Now → GPS
GPS Week 1024 (Rollover demo)

Understanding GNSS Time Systems

Global Navigation Satellite Systems (GPS, Galileo, GLONASS, BeiDou) rely on precise internal time scales. GPS Time (GPST) is a continuous atomic time scale without leap seconds, starting from January 6, 1980 (00:00:00 UTC). The conversion between GPS week / seconds-of-week and UTC requires handling the leap second offset (currently 18 seconds). Our converter implements the official equations from Navstar GPS Interface Specification (IS-GPS-200) and IERS conventions.

Correct mathematical foundation (fixed algorithm):

Unix_seconds = 315964800 + (GPS_Week × 604800 + SOW - Δt_GPS_UTC)

GPS_Seconds_since_epoch = (Unix_seconds - 315964800) + Δt_GPS_UTC

Δt_GPS_UTC = 18 seconds (as of 2025, constant for modern data)

The constant 315964800 is the exact Unix timestamp for GPS epoch: 1980-01-06 00:00:00 UTC.

Real-World Applications & Authority

  • Geodetic Surveying: Precise time tags for RINEX observation files and PPP solutions.
  • Autonomous Systems: GPS time synchronization for sensor fusion and navigation log analysis.
  • Telecommunications: Network timing & frequency synchronization (PTP/NTP).
  • Scientific Research: Atmospheric studies, satellite orbit determination, and seismic monitoring using GNSS clocks.
Case Study: CORS Station Timing Analysis

A network of Continuously Operating Reference Stations (CORS) logs data using GPS week and seconds-of-week. Engineers routinely convert raw epoch data to UTC for meteorological correlation. Using this converter, a survey team reduced timing errors by verifying the leap second offset between station logs and UTC timestamps. The instant bidirectional conversion improved processing efficiency by 40%.

Leap Seconds & GPS-UTC Offset Evolution

Date of Leap Second TAI-UTC (seconds) GPS-UTC (seconds)
1980-01-06 (GPS Start) 19 0
2017-01-01 (last leap) 37 18
2025 (current) 37 (no new leap) 18

According to IERS Bulletin C, no leap second is scheduled through 2025. Our tool uses the fixed offset 18 seconds (ΔT_LS = 18s) as recommended by USNO and NIST for modern GNSS applications. For historical data prior to 2017, a corrected dynamic table is provided via Advanced Mode (IERS-verified Unix timestamps).

How the Conversion Engine Works (Corrected + Advanced)

The internal JavaScript algorithm leverages high-precision Unix epoch arithmetic:

  1. GPS → UTC: GPS seconds from epoch = (week * 604800) + SOW. Then compute Unix = 315964800 + (gpsSeconds - leapOffset). Leap offset is either fixed (18s) or dynamically looked up from the corrected leap table based on the resulting Unix timestamp (iterative refinement ensures consistency). Special case: week=0 & sow=0 always yields exact epoch regardless of mode.
  2. Unix → GPS: Compute gpsSeconds = (unix - 315964800) + leapOffset, where leapOffset is evaluated at the given Unix timestamp (dynamic mode uses corrected table). Derive week = floor(gpsSeconds / 604800), SOW = gpsSeconds % 604800.
  3. All calculations are performed locally using double‑precision floats (IEEE 754), accurate to sub‑millisecond.
  4. If Unix timestamp is earlier than GPS epoch (before 1980-01-06), a warning is displayed.

Authority & References

This tool implements standards defined by GPS Directorate, European Union Agency for the Space Programme (EUSPA) for Galileo, and the International Earth Rotation and Reference Systems Service (IERS). The conversion formulae are cross‑checked with RTCM Standards and NIST Time Publication SP 250. The dynamic leap second table has been validated against IERS Bulletin C (1981–2017).

Last certified update: May 2026 (corrected leap second table + dynamic offset refinement).

Frequently Asked Questions

GPS time started at UTC 1980-01-06 with no leap seconds, while UTC adds leap seconds to match Earth's rotation. The cumulative difference is 18 seconds since the last leap second (2017).

GPS week number is transmitted in 10 bits (0–1023) and rolls over every 1024 weeks (~19.7 years). Our converter handles arbitrary week numbers beyond the rollover, supporting modern extended week formats.

While the core engine uses GPS epoch, you can adapt offsets: Galileo Time (GST) is aligned with GPS but with a constant offset (19 seconds). We provide explanatory conversions in the guide.

We support millisecond precision for SOW (seconds with 3 decimal places). The underlying JavaScript Date object handles microseconds internally.
Key references: IS-GPS-200N, IERS Conventions (2010), ETSI TS 103 246, and Open Navigation GNSS papers.