GPS Week & Time Converter
Convert between UTC date/time and GPS week number, day-of-week, and seconds-of-week.
This field is interpreted as UTC (not local time).
Convert GPS → UTC
What is a GPS week?
A GPS week is a continuous week count used by the Global Positioning System time standard. GPS time starts at midnight on 1980-01-06 (the GPS epoch). Instead of storing a full calendar date, many receivers and satellite systems represent time as:
- GPS Week Number (weeks since epoch)
- Seconds of Week (SOW) (0 to 604,799)
This format is compact, efficient, and ideal for navigation firmware, telemetry logs, and precise timing applications.
How this GPS week calculator works
This tool performs both common conversions:
- UTC → GPS: Returns GPS week, day-of-week, seconds-of-week, and the 1024-week rollover value.
- GPS → UTC: Converts a week and seconds-of-week back to a UTC calendar timestamp.
It also accounts for the GPS-UTC offset caused by leap seconds. GPS time is continuous and does not insert leap seconds, while UTC does. As a result, GPS is currently ahead of UTC by a fixed number of seconds that changes only when leap seconds are introduced.
GPS week rollover explained
Some systems historically stored the week number in only 10 bits, which means the count wraps every 1024 weeks (about 19.7 years). That event is called a GPS week rollover. If a device does not handle rollover correctly, dates may jump backward by decades.
Known rollover milestones
- First rollover: August 1999
- Second rollover: April 2019
- Next rollover (10-bit context): around November 2038
This calculator includes the Week mod 1024 value so you can compare full-week results against rollover-limited systems.
Formula summary
UTC to GPS
GPS seconds = (UTC - GPS epoch) + leap seconds since 1980-01-06
GPS to UTC
UTC seconds = GPS seconds - leap seconds (iteratively solved)
Iteration is necessary because leap seconds depend on the resulting UTC date.
Common use cases
- Parsing GNSS receiver logs
- Validating timing packets in embedded systems
- Converting satellite telemetry timestamps to calendar dates
- Debugging PPS and NMEA timing alignment
- Cross-checking rover/base station observation files
FAQ
Is GPS time the same as UTC?
No. GPS time does not apply leap seconds, while UTC does. That creates a known offset between the two.
Why did my old device show the wrong year?
It may be affected by GPS week rollover logic and interpreting week numbers with only 10 bits.
Can I convert directly from week + day-of-week?
Yes. Multiply day-of-week by 86,400 and add seconds-of-day to get seconds-of-week, then convert.